I'd rather buy windows 10 and have a physical copy on hand, what happens when it comes to having to reinstall? I suppose you could create a drive image but still....
No need. Can download an ISO onto a USB pen drive or DVD, install Win 10, use the Win 7 key to activate, and then keep the pen drive or DVD for any reinstalls or repairs.
https://www.microsoft.com/en-us/software-download/windows10