How to Upgrade from Windows 7 RC to Final Version without Clean Install

Generally speaking, upgrading from a pre-release edition of Windows 7 (e.g. RC 7100) requires a clean install of the system, meaning that you will need to manually reload some files from a backup or other source, and will lose various system settings.

Fortunately, there is a way to bypass this requirement, although you may not want to for compatibility and stability purposes.

The process, as described on this MSDN blog, is as follows:

1. Insert the final-release Windows 7 CD when you purchase it in October
2. Copy the whole image to a storage location you wish to run the upgrade from (a bootable flash drive or a directory on any partition on the machine running the pre-release build).
   Browse to the sources directory.
3. Open the file cversion.ini in a text editor like Notepad.
4. Modify the MinClient build number to a value lower than the down-level build. For example, change 7100 to 7000 (pictured below).
5. Save the file in place with the same name.
6. Run setup like you would normally from this modified copy of the image and the version check will be bypassed.

The “How-To Geek” has further instructions along with screenshots.