I have this old Toshiba Laptop, it came with Windows 7 but I bought a Upgrading key to go up to windows 8 pro. After Installing windows 8 I upgraded to Windows 8.1 pro. I'm building a new computer and I want to know if I could use my Windows 8 key for a Fresh install. If so how would I do it? Since Windows 10 is going to be free for Windows 7 and 8, I don't care if my Laptop will go back to Windows 7. (I am going to format my laptop after all my parts arrive)