Refurbished computer have unwanted "user" folders, can't delete

I bought a refurbished computer, installed with Windows 10.

I have copied the folders/documents into an established user folder (named 'aaaa').

The problem is that there are 2 other user folders ('aa', and 'aaa') which i can't delete, as well as being unable to rename the 'aaaa' folder to something more appropriate.

Each time I try to rename the 'aa', or 'aaa' folders I get "The action cannot be completed... folder or file is open in another program'

There is no rename option for 'aaaa'..

If I try to do anything else with 'aaaa', I get either a warning saying I don't have access. Or a 'permissions' denial with the reference 'S-1-5-21-4185342265-3133696845-3663335998-1001'..

I'm at a loss.