change user name at login

[candygalway]

The user name at login has been entered incorrectly (not sure how/why - it's my Dad's laptop) and I cannot change it. So of course the password doesn't match because the login name is wrong.
How can I get the login screen to prompt me to re-enter the user name? I have the correct username/password. There is no option to change or switch user. I doubt there are any other accounts on the laptop.
Re-booting/shut down-wait-restart just takes me straight back to the previous login name.

Thank you.

 

[RealBeast]

Sorry, forum rules prevent password help. Talk to your Dad about the issue, maybe he can help.