Not able to upgrade ubuntu when typed the command "sudo do-upgrade-release"

[Nakul]

I am currently using Ubuntu 16.04 LTS, and I tried to upgrade to latest Ubuntu 18.04 LTS version using the command I mentioned. However I was not able to do so, since I was getting following error "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'."

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.29 [origin: unknown]
ProcVersionSignature: Ubuntu 4.15.0-76.86~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-76-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Tue Feb 4 16:45:03 2020
InstallationDate: Installed on 2019-01-18 (381 days ago)
InstallationMedia: Ubuntu 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2020-02-04 (0 days ago)