After installing Windows 10 onto your computer, you are given a 30 day period to test out the new version. If you decide that you don't like Windows 10, and would like to revert back to a previous version of Windows within a 30 day period, here is what you have to do:

Step 1: Uninstall and restore

• Open the Start menu, and click Settings.
• Click the Update & Security icon, then select Recovery.
• Depending on your previous version of Windows, select either "Go back to Windows 7" or "Go back to Windows 8.1"
• Click the Get Started button to get rid of Windows 10, and restore the previous version of Windows.
• At this point, you might receive a pop-up from Microsoft, asking you why you are reverting back. Select any option, and click OK.

Step 2: Remove unnecessary files

• Open up the Start menu, and type "disk cleanup" into the search bar.
• Launch the application and click Clean up system files.
• Find "Previous Windows installation(s)" on the list and remove those files.

Unfortunately, it is impossible to revert back to Windows 7 or 8.1 after the 30 day period because Windows automatically deletes the folders needed to reinstall previous versions. You might have to wipe your computer and do a clean install of Windows 7 or 8.1 if you want to get it back. However, there are actions you can take to prevent Windows from deleting the necessary folders before the 30 day period is up:

• Open the File Explorer, and search up these three folder names: "$Windows.~BT", "$Windows.~WS" and "Windows.old".
• Rename these folders.

By renaming these folders, Windows is now unable to delete the files needed to revert back. All you have to do is rename the folders back to their original names, and you can revert back to Windows 7 or 8.1 beyond the 30 day period.