If you are running Ubuntu, today is your lucky day. Ubuntu 10.04 LTS is now out. Check the Ubuntu website if the latest release is available for download. If not yet, it will be available later on today.
If you want to perform an upgrade instead of downloading the ISO image, just press Alt+F2 and type in “update-manager -d” (without the quotes) into the command box.
The Update Manager should open up and tell you: New distribution release ‘10.04’ is available. Click Upgrade and follow the on-screen instructions.