If you just installed windows and wish to change the product key with another follow the stepw below:
1. Click on the Start Button and type: CMD (into the ‘Search programs and files’ field in the Start Menu)
2. The Start Menu will show ‘CMD.exe’,
3. Right-click the CMD.exe file and select .
4. In the CMD window, type: slmgr.vbs -ipk <type your product key here>
5. To activate windows after changing the key, type: slmgr.vbs -ato