To upgrade from Ubuntu 9.10 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 '10.04' is available. Click Upgrade and follow the on-screen instructions.
To upgrade from Ubuntu 9.10 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 -d; and follow the on-screen instructions.
To upgrade from Ubuntu 8.04 LTS on a server system: follow the same instructions as for Ubuntu 9.10, but set Prompt=lts instead of Prompt=normal.
