Microsoft will soon (?) offer a release candidate (RC) version of Windows 7, and those are testing the product already will most likely want to move from the current beta version to the RC version. That said, it's not going to be easy.
The reason is that in real-life, the upgrade path will be from Windows Vista to Windows 7 (Microsoft has already said that XP to Windows 7 will not be an upgrade path; a fresh install will be required). Because of that, and because they want as many people testing the actual upgrade path as possible, Microsoft would prefer users downgrade to a Vista image, then upgrade to the RC.
Of course, they recognize the fact that some people have installed 7, and love it, and made it their production OS. Thus, they have a way to do an upgrade, one that they are giving to Enterprise customers, but if you don't hack a few things, the installer will run a version check and simply tell you the upgrade is not available and exit. Here is what you need to do
- 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.
For techies, this will not be a problem. We would hope those experimenting with Windows 7 are relatively technical. After all, Microsoft warned that the steps outlined above will be necessary for those who wish to move from either the beta or the RC to the released version of Windows 7 (!).