If you're running 7 then 10 will automatically let you know you're eligible to download. Only requirements needed are
A) It's been activated as genuine by a verified 7 COA, if it hasn't you would have been told after 30 days max.
B) You have downloaded the required update on 7 auto or manual updates.
This installs a white windows icon on your taskbar notifications, click it & it will ask you to reserve your free copy. I live in the UK and have done it twice on 7 PRO. Today it did it on 7 home premium immediately after reservation. Thing to remember is that they will not allow a new seperate install, it will install over the existing 7 & call it old version. It needs to as it copies many things that were on it, it is all automatic. No need to enter COA, network settings or transfer files & folders. You can revert to the original OS, 7 or 8 within 1 month. Or do as I did, double drives, 7 on one / 10 on the other. Haven't tried dual boot from a single drive as 10 will download what it wants, when it wants. Don't want to overwork the drive running 7 whilst downloading unknown to me on 10.