I've taken over my wife's Mac mini running osx high sierra. I was in a rush and went into system preferences, clicked on the current user (advanced options), which was named 'user', which was also the administrator, and changed the name to 'grant'. This didn't end up changing the username. I then tried to create another administrator user called 'grant'.
I logged out. When I logged back in the only user available to log in with was 'user'. When I opened user preferences I see that 'user' is no longer an administrator.
I now have no way of accessing an administrator. When I try move files into the applications folder it asks for admin username and password. I've tried every combination of 'user' and 'grant' and nothing works.
Any help getting me access to an admin user will be appreciated.