If you are running Windows 7 Beta and you try to upgrade to Windows 7 RC straight from the installation media, you’ll get an error telling you that this is not possible. Similarly, if you are trying to upgrade from Windows 7 Beta or RC to Windows 7 RTM, you’ll get a similar message.

The upgrade is possible. You just have to do a bit of mucking around. To perform the upgrade, do the following:

1. Copy the contents of the ISO or DVD to a separate storage location (such as a bootable USB storage device, a separate partition or whatever)
2. Open the file \sources\cversion.ini in a text editor and modify the MinClient number to a number lower than the version Windows 7 that you want to upgrade from – so for the beta you would set this to something like 6900.
3. Save the file and then run the install routine from the location with the modified file