Windows 10 (Version 1511 or higher) can be activated using Windows 7, Windows 8, and Windows 8.1 product keys. You can easily activate windows 10 using other windows purchased product activation key.
1. First click on Start then Settings.
2. Then click on Update & security.
3. From the left select Activation and then on the right click on Change product key.
4. Then type your previous Windows OS product key in there carefully and it should activate.