How to upgrade to Windows 10 for free
As CokeRobot explains, you need to choose the upgrade where you keep your files and information. If you choose to do a fresh install, you lose the ability to upgrade to Windows 10 for free, and will need to buy a Windows 10 licence.
To upgrade for free, use the Windows Media Creation Tool and select to upgrade from there. Enter in your Windows 7 (or Windows 8) licence key, and you should soon have a Windows 10 running – for free.