The Ubuntu developers are moving quickly to bring you the absolute latest and greatest software the Open Source Community has to offer. The Jaunty Jackalope Alpha 6 is the sixth alpha release of Ubuntu 9.04, bringing with it a number of new features to improve daily computing.
Note:- This is still an alpha release. Do not install it on production machines. The final stable version will be released on April 23rd, 2009.
Upgrading from Ubuntu 8.10
To upgrade from Ubuntu 8.10 on a desktop system, press Alt+F2 and type in "update-manager -d" (without the quotes) into the command box. Update Manager should open up and tell you: New distribution release '9.04′ is available. Click Upgrade and follow the on-screen instructions.
To upgrade from Ubuntu 8.10 on a server system: install the update-manager-core package if it is not already installed; edit /etc/update-manager/release-upgrades and set Prompt=normal; launch the upgrade tool with the command sudo do-release-upgrade; and follow the on-screen instructions.
You can check here for Jaunty new features
Download Ubuntu 9.04 (Jaunty Jackalope) Alpha 6 from here