If it’s been less than a month since you upgraded to Windows 10, you can go back to your previous version of Windows by going to Settings > Update & security > Recovery  and selecting either Go back to Windows 7 or Go back to Windows 8.1. This won't affect your personal files, but it will remove any apps you installed after the upgrade to Windows 10. Learn more.

If it’s been more than a month, this option won’t be available in Settings and you’ll need to use a different recovery option.