If you have root permission, it is also possible to delete a user, there is a dedicated command for deleting user on xubuntu, just like creating new user, this can be done through command line as well.
The command for deleting user on xubuntu is the 'userdel' command, simply run the command 'userdel' followed by the name of the user.
sudo userdel [username]
sudo userdel john
sudo userdel erin
sudo userdel michael
Alternatively you can also delete user along with the home directory, by adding -r parameter to the 'userdel' command.
sudo userdel -r john
