Instructions
Summary
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.