Because of the free Windows 10 upgrade coming for Starter, Home Basic, Home Premium, Professional and Ultimate Windows 7 and Windows 8.1 editions, I did a downgrade from Windows 8.1 Enterprise to Professional, keeping all my files, applications and settings.
Let's have a look how to do that. Just remember, it's probably not a valid downgrade, but it works perfectly. As long you have a valid product key, nothing illegally is done.
The following Windows versions can upgrade free to Windows 10 Home: Windows 7 Starter, Windows 7 Home Basic, Windows 7 Home Premium and Windows 8.1 editions
The following Windows versions can upgrade free to Windows 10 Pro: Windows 7 Professional, Windows 7 Ultimate, Windows 8.1 Pro and Windows 8.1 Pro For Students editions
The following Windows versions can upgrade free to Windows 10 Mobile: Windows Phone 8.1 only
Guide to downgrade Windows 8.1 Enterprise to Professional:
1. Open regedit.exe and navigate to HKLM\Software\Microsoft\Windows NT\CurrentVersion
2. Change ProductName to Windows 8.1 Professional
3. Change EditionID to Professional
4. Navigate now to HKLM\Software\Wow6432Node\Microsoft\Windows NT\CurrentVersion
5. Change ProductName to Windows 8.1 Professional
6. Change EditionID to Professional
7. Close regedit.exe (no need to restart)
8. Start the Windows 8.1 Pro installation
With that you're done and a free upgrade to Windows 10 Pro is possible! Features missing are Enterprise options like Direct Access and language packs, but I don't miss them on my home PC. Happy upgrading to Windows 10 :-)
Note: This guide will work for Windows 7 and 8 as well.
Update 6-7: When people may experience issues when downgrading, maybe this will help? Windows 7 Downgrader: http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/downgrade-win-7-ultimate-to-win-7-professional/cfebbc77-683a-4d32-bf3a-e897619a82f7
Otherwise it's possible to become an Windows Insider too (without the need to have an official product key): http://blogs.windows.com/bloggingwindows/2015/06/19/upcoming-changes-to-windows-10-insider-preview-builds/
Update 2-8: Joe Donkor mentions:
I ran through this today. I just couldn't get step 8 to work and got the message that the computer was being rolled back to the previous configuration. In desperation after a few tries, I just ran the Win 10 pro install and it worked without issue. So if you get stuck at the same point I did, give it a try. > Just great to hear that! Good try :)
Update: Dirk van Gelderen mentions:
It works (at least in my case) !! Did the regedit tweaks and run the Windows 10 installer and have now an up-and-running Windows 10 (with legal license) computer with all apps, data & settings from Windows 8.1. > Thanks for comment and testing!
Update 14-8: Alessio mentions:
I was facing the same error (Keep only files or nothing). I was able to get around it following the instructions above PLUS this: change ProductName and EditionID respectively to "Windows 8.1 Professional" and to "Professional" in this registry key HKLM\Software\Microsoft\Windows NT\CurrentVersion
You should be able to do the in-place upgrade now :) > Thanks for feedback.
Update 14-8: Mahomed mentions:
This worked for Windows 10 Enterprise down to Windows 10 Pro. I just edited the keys and ran the setup for Windows 10 Pro (without rebooting after changing the registry). Also make sure you've installed all updated and rebooted BEFORE making the registry changes. > Always good to know :) Thanks for comment!
Update 24-8: Anonymous mentions:
I finally had time to use the app to update to windows 10, and want everyone to know it worked flawlessly. I edited the registry, the app showed up the next day, and I used it. > Another way to update!
Note: Thanks for comments everyone! Love it :)
Update 8-9: With the Media creation tool available, free Windows 10 upgrade is still possible. You can download it from HERE.