If you have a legit Windows 7/8.1: 1.) You can upgrade to Windows 10 and it will use the key attached to the BIOS 2.) Clean install should use the key from BIOS. If it asks for a key just enter the key in your BIOS. If you don't know what it is then download a tool to grab it. Plenty info here on that. If you want Windows 10, but aren't using a legit Windows 7/8.1: Sign up to become a Windows Insider. As long as you stay with the Insider program you get access to all the newest preview builds. Leave the Insider program and stay with a build that came from it, your version will switch from a legit Insider preview that's activated to a time-bombed version that will expire. I don't see what people don't understand about it. Microsoft has been telling people what to do, but they aren't going to be crystal clear and detailed about it and say it like I did. People are trying very hard to get them to say "Hey pirates here how you can use a legit build". They know people are trying to force them into saying that so they are changing their wording around. They haven't actually made any changes to anything. People who keep saying that just don't know how to read very well.