In Ubuntu 12.04 and 12.10, to delete an additional user you have created, use the following:
sudo deluser [username]
By example, if we wanted to delete a user we created called “test”, we would run:
sudo deluser test
Which gives:
Removing user `test’ …
Warning: group `test’ has no more members.
Done.
Be careful with this – don’t delete your admin account 🙂