Does the Windows.old folder have a date next to it ?
I don't think it will be from when you first upgraded to Win 10 as Windows was supposed to delete that Windows.old folder after 30 days and 10 - 12 days after a major update.
I don't know what a factory reset will take you back to even if it allows it.
There are Win 10 Refresh and Reset options but if you create Win 10 install media you will be able to perform a repair install which won't affect your personal stuff or your installed programs.
A Refresh won't touch your personal stuff but will remove any 3rd party programs and a Reset will remove the lot.
You can create install media by using the Download tool now button at
https://www.microsoft.com/en-gb/software-download/windows10 but read the instructions first as they differ for using a DVD to an USB.
It's about a 3GB download and has its own burner.
When you've created the media of your choice, open Window Explorer - This PC and with the media inserted, double click on the drive.
If using a DVD this will start the process but if using an USB, that will open the files where you would double click on setup Application.
You can choose to include the updates in the process or leave them until the repair install has completed where they'll auto download/install.
You would need to check if System protection was turned on after and any defaults you had set for say your browser, music, videos or PDFs may need to be reset.