Important: You only have one month from the time you upgraded to Windows 10 to downgrade back to your previous Windows version.

To rollback to a previous Windows version,
  • Log on with an administrator user name and password.
  • Click the Start button and click Settings.
         
  • In the Setting menu, click the Update & security icon.
         
  • In the left navigation of the Update & security screen, click Recovery. In the Recovery pane, locate the section called Go back to Windows 7 (if your old operating system was Windows 8.1, this will say Go back to Windows 8.1 instead). Click the Get started button under this section.
         
  • If you created any new user accounts since upgrading to Windows 10, you will need to completely remove them first before proceeding.
         
  • You may encounter a survey entitled Why are you going back? Make a selection that best suits your reason, and click Next to continue.
         
  • After some convincing arguments to discourage you from proceeding with the downgrade, click the Next button in the What you need to know window.

When your computer next restarts, it will return to the old version of Windows you have chosen.

Source: https://techhelpkb.com/how-to-downgrade-windows-10-to-a-previous-version/