Slightly oddball question and situation: I currently have a Win8.1 (Home) system and will be upgrading to Win10. I know that I can upgrade for free using the Win10 "reservation" and upgrade process (through the Windows upgrade icon in my Notification Area) or separately by downloading the Win10 installation media through the Microsoft website for this. Doing so, I'll end up with Win10 Home. However, I also have a "spare"/unused Win7 Ultimate disk and license key. I was thinking to use that copy and key so as to be able to get Win10 Pro on my system. To do so, could I simply download the Win10 installation media and then do a clean install of that onto my system, using the Win7 license key when prompted for a key? Or would I need to do a clean install of Win7, using the Win7 key for that purpose, and then once that is installed, do a second install, this time of Win10, in which process the Win10 install process would grab the just-embedded Win7 key? And if I needed to go this second route, would I need to do the upgrade to Win10 as an upgrade or could I instead do it as a clean install? Thanks--just thinking that having Win10 could be beneficial, and I do have that extra Win7 key around.