Likely the ROS packages are preventing your upgrade. The installer has produced a list of obsolete packages. You may need to remove the packages, and after the upgrade you can reinstall them if they have been made available for Ubuntu 18.04.

Here is the long list from VarLogDistupgradeMainlog.txt:

code libpyside-py3-2.0 libpyside2-dev libpyside2.0 libshiboken-py3-2.0 libshiboken2-dev libshiboken2.0 python-catkin-pkg-modules python-pyside2 python-pyside2.qtconcurrent python-pyside2.qtcore python-pyside2.qtgui python-pyside2.qthelp python-pyside2.qtnetwork python-pyside2.qtprintsupport python-pyside2.qtqml python-pyside2.qtquick python-pyside2.qtquickwidgets python-pyside2.qtscript python-pyside2.qtsql python-pyside2.qtsvg python-pyside2.qttest python-pyside2.qtuitools python-pyside2.qtwebkit python-pyside2.qtwebkitwidgets python-pyside2.qtwidgets python-pyside2.qtx11extras python-pyside2.qtxml python-rosdep-modules python-rosdistro-modules python-rospkg-modules ros-kinetic-actionlib ros-kinetic-actionlib-msgs ros-kinetic-actionlib-tutorials ros-kinetic-amcl ros-kinetic-angles ros-kinetic-base-local-planner ros-kinetic-bhand-controller ros-kinetic-bond ros-kinetic-bond-core ros-kinetic-bondcpp ros-kinetic-bondpy ros-kinetic-camera-calibration ros-kinetic-camera-calibration-parsers ros-kinetic-camera-info-manager ros-kinetic-catkin ros-kinetic-class-loader ros-kinetic-clear-costmap-recovery ros-kinetic-cmake-modules ros-kinetic-collada-parser ros-kinetic-collada-urdf ros-kinetic-common-msgs ros-kinetic-common-tutorials ros-kinetic-compressed-depth-image-transport ros-kinetic-compressed-image-transport ros-kinetic-control-msgs ros-kinetic-controller-interface ros-kinetic-controller-manager ros-kinetic-controller-manager-msgs ros-kinetic-costmap-2d ros-kinetic-cpp-common ros-kinetic-cv-bridge ros-kinetic-depth-image-proc ros-kinetic-desktop ros-kinetic-desktop-full ros-kinetic-diagnostic-aggregator ros-kinetic-diagnostic-analysis ros-kinetic-diagnostic-common-diagnostics ros-kinetic-diagnostic-msgs ros-kinetic-diagnostic-updater ros-kinetic-diagnostics ros-kinetic-dynamic-reconfigure ros-kinetic-eigen-conversions ros-kinetic-eigen-stl-containers ros-kinetic-executive-smach ros-kinetic-filters ros-kinetic-gazebo-dev ros-kinetic-gazebo-msgs ros-kinetic-gazebo-plugins ros-kinetic-gazebo-ros ros-kinetic-gazebo-ros-pkgs ros-kinetic-gencpp ros-kinetic-geneus ros-kinetic-genlisp ros-kinetic-genmsg ros-kinetic-gennodejs ros-kinetic-genpy ros-kinetic-geometric-shapes ros-kinetic-geometry ros-kinetic-geometry-msgs ros-kinetic-geometry-tutorials ros-kinetic-gl-dependency ros-kinetic-gmapping ros-kinetic-hardware-interface ros-kinetic-hls-lfcd-lds-driver ros-kinetic-image-common ros-kinetic-image-geometry ros-kinetic-image-pipeline ros-kinetic-image-proc ros-kinetic-image-publisher ros-kinetic-image-rotate ros-kinetic-image-transport ros-kinetic-image-transport-plugins ros-kinetic-image-view ros-kinetic-interactive-marker-tutorials ros-kinetic-interactive-markers ros-kinetic-joint-state-publisher ros-kinetic-kdl-conversions ros-kinetic-kdl-parser ros-kinetic-laser-assembler ros-kinetic-laser-filters ros-kinetic-laser-geometry ros-kinetic-laser-pipeline ros-kinetic-librviz-tutorial ros-kinetic-map-msgs ros-kinetic-map-server ros-kinetic-media-export ros-kinetic-message-filters ros-kinetic-message-generation ros-kinetic-message-runtime ros-kinetic-mk ros-kinetic-move-base ros-kinetic-move-base-msgs ros-kinetic-moveit-msgs ros-kinetic-nav-core ros-kinetic-nav-msgs ros-kinetic-navfn ros-kinetic-nodelet ros-kinetic-nodelet-core ros-kinetic-nodelet-topic-tools ros-kinetic-nodelet-tutorial-math ros-kinetic-object-recognition-msgs ros-kinetic-octomap ros-kinetic-octomap-msgs ros-kinetic-opencv3 ros-kinetic-openslam-gmapping ros-kinetic-orocos-kdl ros-kinetic-pcl-conversions ros-kinetic-pcl-msgs ros-kinetic-pcl-ros ros-kinetic-perception ros-kinetic-perception-pcl ros-kinetic-pluginlib ros-kinetic-pluginlib-tutorials ros-kinetic-polled-camera ros-kinetic-pr2-msgs ros-kinetic-pr2-power-board ros-kinetic-py-trees ros-kinetic-py-trees-msgs ros-kinetic-python-orocos-kdl ros-kinetic-python-qt-binding ros-kinetic-qt-dotgraph ros-kinetic-qt-gui ros-kinetic-qt-gui-cpp ros-kinetic-qt-gui-py-common ros-kinetic-qwt-dependency ros-kinetic-random-numbers ros-kinetic-resource-retriever ros-kinetic-robot ros-kinetic-robot-model ros-kinetic-robot-state-publisher ros-kinetic-rocon-console ros-kinetic-rocon-python-utils ros-kinetic-rocon-service-pair-msgs ros-kinetic-rocon-std-msgs ros-kinetic-ros ros-kinetic-ros-base ros-kinetic-ros-comm ros-kinetic-ros-core ros-kinetic-ros-environment ros-kinetic-ros-tutorials ros-kinetic-rosbag ros-kinetic-rosbag-migration-rule ros-kinetic-rosbag-storage ros-kinetic-rosbash ros-kinetic-rosboost-cfg ros-kinetic-rosbuild ros-kinetic-rosclean ros-kinetic-rosconsole ros-kinetic-rosconsole-bridge ros-kinetic-roscpp ros-kinetic-roscpp-core ros-kinetic-roscpp-serialization ros-kinetic-roscpp-traits ros-kinetic-roscpp-tutorials ros-kinetic-roscreate ros-kinetic-rosgraph ros-kinetic-rosgraph-msgs ros-kinetic-roslang ros-kinetic-roslaunch ros-kinetic-roslib ros-kinetic-roslint ros-kinetic-roslisp ros-kinetic-roslz4 ros-kinetic-rosmake ros-kinetic-rosmaster ros-kinetic-rosmon-msgs ros-kinetic-rosmsg ros-kinetic-rosnode ros-kinetic-rosout ros-kinetic-rospack ros-kinetic-rosparam ros-kinetic-rospy ros-kinetic-rospy-tutorials ros-kinetic-rosserial-msgs ros-kinetic-rosserial-python ros-kinetic-rosservice ros-kinetic-rostest ros-kinetic-rostime ros-kinetic-rostopic ros-kinetic-rosunit ros-kinetic-roswtf ros-kinetic-rotate-recovery ros-kinetic-rqt ros-kinetic-rqt-action ros-kinetic-rqt-bag ros-kinetic-rqt-bag-plugins ros-kinetic-rqt-bhand ros-kinetic-rqt-common-plugins ros-kinetic-rqt-console ros-kinetic-rqt-controller-manager ros-kinetic-rqt-dep ros-kinetic-rqt-drone-teleop ros-kinetic-rqt-ez-publisher ros-kinetic-rqt-gauges ros-kinetic-rqt-graph ros-kinetic-rqt-ground-robot-teleop ros-kinetic-rqt-gui ros-kinetic-rqt-gui-cpp ros-kinetic-rqt-gui-py ros-kinetic-rqt-image-view ros-kinetic-rqt-joint-trajectory-controller ros-kinetic-rqt-joint-trajectory-plot ros-kinetic-rqt-launch ros-kinetic-rqt-launchtree ros-kinetic-rqt-logger-level ros-kinetic-rqt-moveit ros-kinetic-rqt-msg ros-kinetic-rqt-multiplot ros-kinetic-rqt-nav-view ros-kinetic-rqt-plot ros-kinetic-rqt-pose-view ros-kinetic-rqt-pr2-dashboard ros-kinetic-rqt-publisher ros-kinetic-rqt-py-common ros-kinetic-rqt-py-console ros-kinetic-rqt-py-trees ros-kinetic-rqt-reconfigure ros-kinetic-rqt-robot-dashboard ros-kinetic-rqt-robot-monitor ros-kinetic-rqt-robot-plugins ros-kinetic-rqt-robot-steering ros-kinetic-rqt-rosmon ros-kinetic-rqt-runtime-monitor ros-kinetic-rqt-rviz ros-kinetic-rqt-service-caller ros-kinetic-rqt-shell ros-kinetic-rqt-srv ros-kinetic-rqt-tf-tree ros-kinetic-rqt-top ros-kinetic-rqt-topic ros-kinetic-rqt-web ros-kinetic-rqt-wrapper ros-kinetic-rviz ros-kinetic-rviz-plugin-tutorials ros-kinetic-rviz-python-tutorial ros-kinetic-self-test ros-kinetic-sensor-msgs ros-kinetic-shape-msgs ros-kinetic-simulators ros-kinetic-slam-gmapping ros-kinetic-smach ros-kinetic-smach-msgs ros-kinetic-smach-ros ros-kinetic-smclib ros-kinetic-stage ros-kinetic-stage-ros ros-kinetic-std-msgs ros-kinetic-std-srvs ros-kinetic-stereo-image-proc ros-kinetic-stereo-msgs ros-kinetic-tf ros-kinetic-tf-conversions ros-kinetic-tf2 ros-kinetic-tf2-eigen ros-kinetic-tf2-geometry-msgs ros-kinetic-tf2-kdl ros-kinetic-tf2-msgs ros-kinetic-tf2-py ros-kinetic-tf2-ros ros-kinetic-theora-image-transport ros-kinetic-topic-tools ros-kinetic-trajectory-msgs ros-kinetic-turtle-actionlib ros-kinetic-turtle-tf ros-kinetic-turtle-tf2 ros-kinetic-turtlesim ros-kinetic-unique-id ros-kinetic-urdf ros-kinetic-urdf-parser-plugin ros-kinetic-urdf-tutorial ros-kinetic-uuid-msgs ros-kinetic-variant-msgs ros-kinetic-variant-topic-tools ros-kinetic-vision-opencv ros-kinetic-visualization-marker-tutorials ros-kinetic-visualization-msgs ros-kinetic-visualization-tutorials ros-kinetic-viz ros-kinetic-voxel-grid ros-kinetic-webkit-dependency ros-kinetic-xacro ros-kinetic-xmlrpcpp shiboken2 singularity-container zoom