Check out http://windows7news.com/2009/04/27/upgrading-from-windows-7-rc-to-final/ for a fairly logical and believable answer to the question of upgrading from RC to RTM. The pertinent text is shown below: The only official indicator that upgrading from Windows 7 release candidate to Windows 7 final will be possible can be found in the Engineering Windows 7 blog post about upgrading from beta to release candidate. You might remember the post as it gives instructions on how to override the upgrade protection. One of the last sentences of that article is the following:These same steps will be required as we transition from the RC milestone to the RTM milestone. The steps that were outlined for upgrading the Windows 7 beta release to release candidate were the following: Download the ISO as you did previously and burn the ISO to a DVD.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.Open the file cversion.ini in a text editor like Notepad.Modify the MinClient build number to a value lower than the down-level build. For example, change 7100 to 7000 (pictured below).Save the file in place with the same name.Run setup like you would normally from this modified copy of the image and the version check will be bypassed. It is furthermore very likely that the rtm build of Windows 7 will be distributed with the build number 7200. An upgrade from release candidate to rtm build would therefor require the modification of the MinClient build number from 7200 to 7100 or lower. This would in theory mean that it could also be possible to upgrade Windows 7 Beta to Windows 7 RM using the same procedure.