Trying to delete users

I am trying to delete a user to look at selling my Imac, it is currently running 10.15.4, its a 21.5 late 2013 model, 2.7 GHz Quad-Core Intel Intel i5 8gb Ram.

When I log in to Users & Groups with all users except myself logged out padlock unlocked, I highlight the one to be deleted click the - sign but nothing happens after that I have waited for more than 10 mins. I have tried to restart the Imac and still no joy I created an new user but cant delete that either!!

I know everything seems slow on it but I would of expected it to show up the delete options before 10 mins.

Can anyone please assist with this further?

Regards, Wyn