Change windows product key after installation

Sometimes, from some reasons, we need to change product key when installation is already done. There are two ways:

  1. From CMD prompt
    Type: slmgr.vbs -ipk xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
  2. From graphical interface
    In CMD prompt type: slui.exe 3.
    Type in your product key and click the Activate button in a form.