How to Downgrade from Windows 10 Pro to Windows 10 S
If you ask me, Windows 10 S hobbles computers, preventing you from using apps outside of the Windows Store. But if you upgraded your Surface Laptop or other Windows 10 S device to Windows 10 and, for some reason, want to restore it to Windows 10 Pro, it is possible.
Paul Thurrot points out that a downloadable recovery image of Windows 10 S is now available on the Surface website. You'll have to insert your serial number from your registered Surface Laptop, but after that you should be ready to restore. Additionally, you could make a recovery drive prior to upgrading your OS.
From there, you'll want to reset your Windows 10 PC. You can find instructions here, but you'll want to duck into the advanced startup options instead of going for a full recovery through the menu. That will give you the option to use your Windows 10 S recovery drive.
Microsoft has publicly stated that the Windows 10 S to Windows 10 Pro transition is a permanent one: "Switching to Pro is one-way," a FAQ for Windows 10 S reads. "If you make the switch, you won't be able to go back to Windows 10 S."
It's true in that you can't switch back via a downgrade button in the system, but if you download the recovery system, you should be back to your limited computing environment in no time.
Windows 10 Annoyances and Problems