I am trying to update my old ubuntu to the latest version

[deepti mittal]

(appstreamcli:5810): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:5810): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed

(appstreamcli:5810): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:5810): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed

(appstreamcli:5810): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:5810): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed
AppStream cache update completed, but some metadata was ignored due to errors.

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating the changes

Calculating the changes

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

If none of this applies, then please report this bug using the
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.If
you want to investigate this yourself the log files in
'/var/log/dist-upgrade' will contain details about the upgrade.
Specifically, look at 'main.log' and 'apt.log'.

Restoring original system state

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.30
ProcVersionSignature: Ubuntu 4.4.0-179.209-generic 4.4.219
Uname: Linux 4.4.0-179-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.23
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sat May 9 02:13:55 2020
InstallationDate: Installed on 2016-06-01 (1437 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2020-05-09 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2020-05-09T01:46:38.093536