Microsoft made it easy to jump from an older version of its operating system to one of the Windows 8 previews, but the company has been upfront about one inherent drawback: folks running beta builds won't be able to experience the final version of Windows 8 without a fresh install -- at least not officially.
Although that burdens end users with reconfiguring everything, upgrades aren't perfect, so it helps ensure that everyone has the most stable experience possible around the launch of Windows 8.
Naturally, many experienced users would rather throw caution into the wind and perform the upgrade anyway, so IT admin Denny Cherry ("Mrdenny") has posted a simple workaround that'll let you shift from any of the early builds to the Windows 8 RTM released last week on TechNet and MSDN.
In the worst-case scenario, if the migration is unsuccessful, you'll have to install a clean version of Windows 8 anyway, so there's not much to lose, though you should back up important data before proceeding.
The trick is as simple as editing an INI file which sets the minimum build that the Windows 8 RTM installer can overwrite. This file is named "cversion.ini" and it's located in the RTM's "sources" directory (you'll see the folder if you open the ISO or any other installation media with a file browser, though the data will obviously have to be on a writeable medium to make the changes). Once you find cversion.ini, open it with a text editor and change the two numbers from 8508 to 7100. That's all there is to it. You should able to upgrade to the RTM from the Consumer Preview, Release Preview and other betas.
https://www.techspot.com/news/49880-workaround-lets-you-upgrade-from-windows-8-betas-to-the-rtm.html
