There seems to be a lot of different answers and a lot of chaos going on so I wanted to see if someone who is really familiar with Microsoft leaks in the past can answer my question. I have a legitimate, purchased from M$ retail key for Windows 8 Pro. Since Windows 8.1 RTM is a free upgrade/update for Windows 8 users, can I download a fresh copy of the Windows 8.1 RTM and INSTALL AND ACTIVATE it with that same Windows 8 key... If I have to install with a different key and then change the key via command prompt to activate, can someone tell me why this is? Thank you for the answers!