Ubuntu 12.04 LTS is in its final beta. If you haven't yet downloaded your final beta copy, head towards this page to get one. This is Beta 2 which will give you an preview of the next series of LTS version from Canonical. You can also upgrade your current Ubuntu system running Ubuntu 11.10 or 10.04 LTS.(Desktop Version)
On your Ubuntu desktop press Alt + F2 and type "update-manager -d" (without quotes) right on to the command box.
This will invoke the Update Manager and you will see a message that says " New Distribution Release 12.04 is Available".
Click on Upgrade and follow the instructions thereon. The process may vary as per your broadband strength.