What error did you get when you tried to delete that user? I assume that you have set up a different (Admin) user and tried the delete from that user account.

Have you tried enabling the Hidden Admin User Account, and deleting the unwanted user account from that account?

Possibly useful links:

https://www.howtogeek.com/132428/eve...-windows-8-pc/

https://answers.microsoft.com/en-us/...9-ebba0b7531bb