Comment 8 for bug 1313165

Francois, I am not a "techie" but I'll try to describe the procedure:

from the desktop you will have to start a terminal-session.
Start Applications menu -> Accessories -> Terminal. Or use the keyboard shortcut Ctrl + Alt + T

then from the command-prompt type:

sudo apt-get remove update-manager-kde <ENTER>

type in your password when asked

When finished removing kde return to the desktop and start the scan for updates again. When the scanning is finished you'll see a big button for the availability of the 14.04 version. Click it and follow the procedure. In my case this process was halted before because of the kde-manager being installed. After kde was removed the upgrade worked fine. The upgrade-process might take some hours.