I use Ubuntu in virtual machine. My current version of Ubuntu is 14.04, I want to upgrade it to the latest version which is 16.04.
I opened Software Updater, it checked for update and said:
The software on this computer is up to date, however Ubuntu 16.04.1 LTS is now available.
So I clicked the upgrade button and entered my password.
BUT it failed, nothing happened.
I repeated a couple of times, still the same result.
Any idea how to fix this?