When I try to enter a user password to delete an account, it doesn't work. and I know the password I'm using is correct
If you can't delete the user for some reason, you can remove it at the command line.
Launch "Terminal" (from /Applications/Utilities/Terminal.app, or search via Spotlight) and type:
sudo dscl . list /Users
...followed by your administrator password. Then hit enter
The output will show you the shortname of your local users (towards the bottom). Here I called the user to be removed "testy" (I'm only showing the last few entries):
...
admin
daemon
Guest
nobody
root
testy
Now remove the user from your system and from System Preferences (exchanging the shortname "testy" with your own, found earlier):
sudo dscl . delete /Users/testy
Then hit enter.
The home folder of that user you can either keep, if there are important files, or delete it with...
sudo rm -r /Users/testy
...and again hit enter.
PS. A speculative answer for the permissions error received and mentioned in the comments section can be found at StackExchange: What causes eDSPermissionError when running dscl?
The bold text is a misnomer and likely a bug, see the smaller text underneath. The prompt requires an administrator username and password, i.e. your credentials not that of the account you’re trying to delete.
I had this problem and fixed it.
- From the Users & Groups panel, right click the user in the list to get Advanced Options...
- I Removed the Apple ID and changed the account name (I don't know which did the trick.)
- Click OK and restart
- Go back to Users & Groups and delete the account with the minus sign box, as usual