Microsoft will allow you to rollback your Windows 10 installation to the previous operating system for 30 days post-upgrade. Security for your data, it is best to use backup tool like EaseUS Todo Backup Free to back up your data before you restore OS.
Officially, from Microsoft Corporation this is a no-go area. The company expects users to be familiar with the new OS within 30 days and hence, feels that there is no need to continue to provide the rollback option. What Windows 10 simply does is that after 30 days it deletes the Windows.old along with $Windows.~BT, and $Windows.~WS. These folders are crucial for a rollback to work.
Downgrade From Windows 10 After 30 Days
One such procedure as outlined by (http://www.thewindowsclub.com/rollback-windows-10-after-30-days ) is to rename all the three folders to something memorable as soon as users upgrade to Windows 10. This way the new OS will not be able to delete these files. After the 30-day time lapse, users can rename these folders and head in "Settings" menu and click on "Update & Recovery." This is not a tried and tested method by us but if this works for someone, do mention it in the comments.
The 3rd-party tools available for Windows 10 rollback. To revert to the original Windows after 30 days a couple of backup software will be able to do the trick. However, users would require an external storage device for the complete backup.
We were also contacted by the team at EaseUS, to take a look at their Windows 10 rollback option. Labeled as specifically EaseUS System GoBack (http://www.easeus.com/system-go-back/), it is aimed at users looking to downgrade from Windows 10, the free software functions in a similar way to the backup tools available already.