This is a recent email to the ubuntu-devel mailing list that describes not only recent changes to the do-release-upgrade process, but how it works in general. It is also posted here.
If you are unaccustomed to the command-line...first of all, you should learn the command line. But for now, the do-release-upgrade utility is used to upgrade from one Ubuntu release to another. The graphical desktop utility utilizes this as well.