Unwanted guest user

Go to System Preferences > Users and Groups > Click the lock on the bottom left corner and enter the username and password of an admin of the computer > Click the Guest User option > Uncheck the "Allow guests to got in to this computer".

Roda007 wrote:

How can I remove an unwanted guest user from my computer.

In order to remove any user, you need admin privileges and the user has to be logged out.

Delete a user or group on Mac - Apple Support