So I have solved this issue, but now I have another problem: An unresolvable problem occurred while calculating the upgrade. This can be caused by: * Upgrading to a pre-release version of Ubuntu * Running the current pre-release version of Ubuntu * Unofficial software packages not provided by Ubuntu If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. I am not upgrading to a pre-release version of Ubuntu and I am not running a pre-release either. I have unchecked all my 3rd-party packages using Ubuntu Software Manager, EditSoftware Sources... What else might be wrong? UPDATE After doing sudo update-manager -d and sudo apt-get update;sudo apt-get dist-upgrade as per JimB's post, and then running sudo do-release-upgrade, here what I get: Err http://extras.ubuntu.com trusty/main Translation-en Err http://extras.ubuntu.com trusty/main Translation-en_US Err http://extras.ubuntu.com trusty/main Translation-en Ign http://extras.ubuntu.com trusty/main Translation-en_US Ign http://extras.ubuntu.com trusty/main Translation-en Fetched 0 B in 0s (0 B/s) Checking package manager Reading package lists... Done Building dependency tree Reading state information... Done Building data structures... Done Calculating the changes Calculating the changes Could not calculate the upgrade An unresolvable problem occurred while calculating the upgrade. This can be caused by: * Upgrading to a pre-release version of Ubuntu * Running the current pre-release version of Ubuntu * Unofficial software packages not provided by Ubuntu If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. Restoring original system state Aborting Reading package lists... Done Building dependency tree Reading state information... Done Building data structures... Done === Command detached from window (Mon Aug 18 23:53:10 2014) === === Command terminated with exit status 1 (Mon Aug 18 23:53:10 2014) ===