If you recently upgraded to Windows 10 and want to back to Windows 7 or Windows 8/8.1, Windows 10 has a special function for this. However, it only works if you upgraded to Windows 10, not if you performed a clean installation.
Go to the “Start” menu => Settings
Update & Security
Then select “Recovery”. You will see the option “Go back to Windows 7” or “Go back to Windows 8/8.1” depending on the version you upgraded from. Click “Get started” and the system will begin the rollback process to the previous version of Windows.