If you try putting an MSDN key into Anytime Upgrade, it will get started on the upgrade process then eventually fail telling you the key you entered cannot be used for Anytime Upgrade. The trick is to use some other key for the same version. This key, though, does not have to activate. I wanted to upgrade from Home to Professional. Luckily I had my Dell Laptop came with Windows 7 Professional.
- Run Anytime Upgrade with any key for the version you want to upgrade to (OEM keys work)
- After the computer restarts and updates, run slmgr.vbs /cpky to delete the product key
slmgr.vbs is available on the internet, on Professional machines, and is probably located somewhere on the install medium
- Run slmgr.vbs /ipk XXXX-PRODUCT-KEY-HERE-XXXX
- Now slmgr.vbs /ato to activate it
** Each command may take a few minutes to finish even though it looks like it goes through instantly. A dialogue box will open with the results when the command has actually completed.
I highly recommend making a disk image before trying this process in case something breaks in the process. You can use Clonezilla, Acronis, Norton Ghost, among many other programs. There are plenty of guides online