If you upgraded to Windows 10 recently and want to go back to Windows 8.1, here are some things you can try. This info only applies if you had Windows 8.1 on your computer before you upgraded. If your computer came with Windows 10 installed, no earlier version of Windows was ever on it. In that situation, you can't go back to Windows 8.1. Note: The option to go back to your previous version of Windows is available only for a limited time following the upgrade (10 days, in most cases).
Select the Start button > Settings > Update & Security > Recovery. Under Go back to the previous version of Windows 10,Go back to Windows 8.1, select Get started. By following the prompts, you'll keep your personal files but remove apps and drivers installed after the upgrade, plus any changes you made to settings.
Try restoring your PC to its factory settings. This reinstalls Windows 8.1 if it came with your PC. It also removes personal files, apps, and drivers you installed, as well as any changes you made to settings. Select the Start button > Settings > Update & Security > Recovery > Reset this PC > Get started, then select Restore factory settings.
If you have a product key for your previous version of Windows, use the media creation tool to create installation media for Windows 8.1, and then perform a clean install of Windows. If you need help finding your key, see Find your Windows product key.
If you're past the 10-day rollback window, or if you'd prefer in any case to fix your Windows 10 installation instead of rolling back, see Reset or reinstall Windows 10.