Upon login, your Ubuntu system may notify you of a new release available. If you’re running Ubuntu 10.04 LTS, you will be notified of “Precise Pangolin” Ubuntu 12.04 LTS. The command for upgrading is “do-release-upgrade“.
The official documentation for this upgrade process is at https://help.ubuntu.com/12.04/serverguide/installing-upgrading.html
I’ve heard the upgrade process is pretty smooth, but haven’t personally tried it yet. I’m guessing for stock Ubuntu with little to no customization the chances of a clean upgrade would be better than highly customized installs.