Upgrading Windows 7 from Beta to Release Candidate

This is actually very easy.

Copy all the files from the Release Candidate DVD into a directory on your hard disk. Go into that directory, look in the “sources” sub-directory for a file “cversion.ini”.
Change the line
and save it.

Burn a new DVD from the directory containing everything, and use that to upgrade your Windows 7 Beta system to Windows 7 Release Candidate.

This information is available officially from Microsoft, but I forget where.