How to downgrade from Windows 10 to Windows 7 or 8.1
After you have upgraded to Windows 10 from Windows 7 or 8.1, you may want to uninstall Windows 10 and downgrade your computer back to the original Windows 8 or 8.1 operating system, according to howtogeek.
Return to Windows 7 or 8.1
If you have upgraded a computer to Windows 10 (not a new one), you will have an easy option to go back to the latest version of Windows. To access this feature, open the Start menu and select Settings. Click the Update & security icon and select Recovery.
You will see a "Go back to Windows 7" or "Go back to Windows 8.1" option. Now click the Get started button to exit Windows 10 and restore the previously installed Windows. Microsoft will ask you why you want to go back to the old operating system.
If you decide to go back to the original version more than a month ago, or if you have already run the Disk Cleanup tool and removed the Previous Windows installations, or if you manually deleted the C: \ Windows.old folder, you will This option does not appear anymore. Windows 10 appears to automatically remove the old Windows installation files after 1 month to free up space.
Use the Windows.old directory
This is done because during the upgrade to Windows 10 pro product key, the old Windows data will be stored in a folder named C: \ Windows.old. You can see this folder in File Explorer, but you should not delete them from here, instead browse through the Windows.old folder and restore files from it.
Obviously, storing files from old Windows will take up a lot of space. If you open the Disk Cleanup application, you will see the amount of space it occupies on your hard disk. Click the Start button, type Disk cleanup to find it, launch it, and click the Clean up system files button.
Looking for Previous Windows installation (s) in the list, you will see how much space it needs to occupy on your hard drive. If you do not want to go back to previous versions of Windows, use the Disk Cleanup tool to remove those files and free up space on your hard disk.
Downgrade if Windows 10 does not offer the option
Suppose you have an older PC that has upgraded to Windows 10, and that machine previously had Windows 7 or 8.1 installed. That means that the computer will come with a product key that allows you to use Windows 7 or 8.1. To return to the older version of Windows, you will have to perform a fresh installation of Windows, however you also need to have knowledge in the installation operation.
You can then boot from it and install new Windows 7 product key or 8.1, with the requirement to overwrite the existing Windows 10 system on the hard drive. Make sure that you have made a backup of all important files of your previous Windows 10 computer to restore it when needed.
You will need to look to the product key on the computer if you do this. On a Windows 7 machine, check the computer for a "Certificate of authenticity" sticker, and it will come with the operating system key. They can be placed under the laptop, in the battery bay, under the removable battery ... On a Windows 8 machine, you probably do not need to do this if the key is embedded in the PC's firmware, and Windows 8.1 will automatically play Execute it, then allow you to reinstall without having to enter the product key.
If you buy a new computer with Windows 10 and want to go back to the previous version of Windows will be more difficult. To do this legally, you will have to purchase a license to use Windows 7 or 8.1 and install it from scratch, then enter the product key you purchased during the installation process.