This steps will guide you to upgrade your Ubuntu 14.10 to 15.04.
Open the “Software & Updates” Setting in Systemsettings.
- Select the 3rd Tab called “Updates”.
- Set the “Notify me of a new Ubuntu version” dropdown menu to “For any new version”.
- Press Alt+F2 and type in “update-manager” (without the quotes) into the command box.
- Update Manager should open up and tell you: New distribution release ‘15.04’ is available.
- Click Upgrade and follow the on-screen instructions.