Today marks the release of new Ubuntu Release 15.10, which a lot of users would like to upgrade to the new version. The upgrade process is so easy and forwarded you will be notified to upgrade after you update your current system. But in case you did not notify or you want to upgrade to a development version, just apply these commands in a terminal.
To upgrade to the next stable release:
To upgrade to the next development release:
sudo do-release-upgrade -d
And you are good to go, just press enter once the upgrade is ready and leave the system to upgrade :)