How to go back to a previous version of Windows after Windows 10 has been installed.

Windows 10 comes with a Go Back feature that gives you a 30 days window to go back to your previous version of Windows (Windows 7 or Windows 8.1) - or a previous build of Windows 10 - if you need or want to do so after upgrading.

IMPORTANT:

• You can only perform this operation within the first 30 days following the upgrade to Windows 10.
• You can only perform a rollback to your previous version of Windows if you installed Windows 10 as an upgrade from Windows 7 or Windows 8.1. Full installations of Windows 10 "from scratch" will only let you return to previous builds of Windows 10.
• If you were using a password to sign into your Windows 7 or 8.1 session, make sure you know that password.
• If you haven't already done so before upgrading to Windows 10, we strongly recommend making a backup of all your data before you start the downgrading process.
• Applications installed (or removed) after the Windows 10 upgrade will need to be re-installed.
• Any system or settings changes made to the computer after the Windows 10 upgrade will be lost.
• If you ran into a low disk space scenario and used an external USB storage to complete the original upgrade to Windows 10, you will need the same USB storage device to perform the Go back procedure.

1. Start by opening the Start menu and selecting Settings.
   
2. In the Settings menu, select Update & security.
   
   
3. Select Recovery in the left pane. You will see 3 options:
   
   
   1. Reset this PC: Delete everything and reinstall Windows 10.
   2. Go back to [your previous version of Windows]: This will restore your previous version of Windows.
   3. Advanced Startup: Here you can change your PC startup settings, restore Windows from a system image, boot from a disc or USB device, etc.
      
      
      
      
4. Select Get Started under Go back to [your previous version of Windows]. Microsoft will then ask for your feedback about Windows 10.
   
5. Follow the on-screen instructions and select Go back to Windows 7/8.1.

WARNING: There is a risk of data loss. Do not turn off or unplug your computer during the downgrading process.

The rollback process will then begin. The amount of time needed will depend on the data that is stored on your computer, your hardware's performance, etc. It can be anything between 10 minutes and several hours. 

NOTE: After the 30 day window has passed, the Go Back feature will no longer appear in the Update & security screen.

Once the rollback is completed, your PC will automatically restart and load your previous version of Windows.

IMPORTANT: The Go back feature can fail if one or more of the following is true:

• The computer is running on battery. The computer must be plugged in and receiving AC power.
• A Refresh procedure has been performed.
• A Reset procedure has been performed.
• The Disk Cleanup (windows.old or .~bt) directory has been edited.
• Files have been manually deleted from windows.old or .~bt directories, or the entire directories have been deleted.
• A new user account has been added (promoting local account to a Microsoft Account not included).

If the Go Back feature is not available, you will need to perform a system recovery .