[ubuntu] Updating from Ubuntu 14.04 LTS

16.04 won't be released till the 21st of April. Until then it remains a development release and should only be used if you are prepared to deal with breakage.

Installing with a 16.04 DVD and selecting "Something Else" at the partitioning screen will allow you to mount the existing 14.04 / partition/disk to install directly over the 14.04 release, by not marking for formatting you will preserve your /home folder. In any event, something as risky as upgrading an operating system shouldn't be done without having a backup of your important data safely secured.

Open up Software Sources and check that you are set to be notified of Long Term release and you will be advised when it is available for you.