How do I delete playlists off of an ipod nano that are not in my itunes account?

My son took my younger son's ipod to his friends house and added about 7 playlists from their itunes account. My son's itunes account on our computer doesn't see them. There are duplicate songs all of the place and we now cannot add any songs to the ipod.
How do I delete playlists off of an ipod nano that are not in my itunes account?
plug the ipod into the computer and open up itunes. then click on the ipod on the left hand column and you should see the playlists being displayed, just right click on them and click delete. (click on the arrow next to where it says ipod on the left hand column if you don't see anything under it)