If you want to you can roll back to Windows 7 or 8.1 whichever the system was previously. You have 30 days from the install of Windows 10, then the Windows old or previous version will be deleted.
More on how to roll back here :-

https://techingiteasy.wordpress.com/2015/03/24/how-to-rollback-to-a-previous-version-of-windows-from-windows-10/