When you install Office 2010, you need to have a valid key to use it after the trial period. In case you have activated it with a valid key and at a later point of time, if you want to change the product keys, Office 2010 does not provide a direct interface to change it. To change the product keys, you need to run the installer and you can do it in 2 ways. Both of them actually involve the same method, but different ways to arrive at it.
