Activation helps verify that your copy of Windows is genuine and hasn’t been used on more devices than the Microsoft Software License Terms allow.
Uninstalling a retail product key on a PC can be useful if you wanted to sell or give the PC away with Windows 10 still installed by not activated, or if you just wanted to use the product key to activate Windows 10 on another PC.
Uninstalling the product key on a Windows 10 PC will not remove the digital license for that PC from Microsoft activation servers.
If you try to activate Windows 10 on another PC with this same retail product key, you may have to activate by phone if online activation fails.
This tutorial will show you how to uninstall the product key on a PC to deactivate Windows 10.
You must be signed in as an administrator to be able to uninstall the product key.
An OEM PC with UEFI firmware will have its product key permanently embedded in the firmware chip. It can't be removed.
EXAMPLE: Windows 10 not activated after uninstalling product key
1 Open an elevated command prompt.
2 Copy and paste the slmgr /upk command into the elevated command prompt, and press Enter to uninstall the product key.
3. Click/tap on OK when the product key has successfully been uninstalled.
4. Copy and paste the
slmgr /cpky command into the elevated command prompt, and press enter key.
This will clear the previously installed product key from the registry so that it can no longer be viewed by product key finder programs like ShowKeyPlus.
This will not remove an OEM product key embedded in the UEFI firmware chip.
Click/tap on OK when the product key has successfully been cleared from the registry.
Article taken from: https://www.tenforums.com/tutorials/35979-uninstall-product-key-deactivate-windows-10-a.html