Depends.............
1. If you have not deleted the Windows.old.
2. If you installed Windows 10 less than 30 days ago.
If you meet the above requirements, you can roll back to your previous Windows operating system by..................
left click at Start button > left side, click Settings > click Updates and Security > left side, click Recovery > the "Roll back" option will be listed at the right side > click Get Started button underneath.