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.