When you try to change your product key from settings sometimes you may receive an error about the key not work so in this case you will need to change the product key via CMD:
First you need to open CMD and enter following command:
slmgr.vbs /ipk KEY
Please replace the “KEY” with the product key received from us.
So, your product key will be changed successfully.
If you receive an error state “Error: 0xC004F069 on a computer running Microsoft Windows non-core edition, run ‘slui.exe 0x2a 0xC004F069′ to display the error text.” That means you probably have the Windows 10 Home edition and trying to upgrade to Windows 10 Pro.
Unfortunately, non-core editions can’t be upgraded to Windows 10 Pro directly so you need to reinstall Windows 10 Pro with clean installation.
You can check here for clean installation instructions as a guide.