Windows 7 has a specific command to change the serial number without having to format or reinstall Windows 7.
It’s more practical if you were still in demo version but you just bought your final version, or you already have your version, but your boss just gave you a license for work.
Here is a very simple command to make in order to change its product key without reinstalling Windows.
Start a command prompt as administrator
To change the product key, type the command:
slmgr -ipk xxx-xxx-xxx-xxx
Replace xxx by your license key
To activate Windows
It’s over you just changed your license Windows 7 and activate it