I have Windows and Ubuntu 12.04 running. I wanted to upgrade to 15.04, but the upgrade manager doesn't give that option. I tried How to install software or upgrade from an old unsupported release? but, it gives me a 404 error. How do i upgrade without affecting the existing partitions on my system adversely.
ANSWER: 12.04 isn't an EOL release. Thanks Arronicle and frkaiem for pointing it out
do-release-upgrade
. – fkraiem Dec 22 '15 at 11:06