OK so I went looking and here is how.

Ok up top click on music (that is in the yellow box up top in the pic). Then go to "my music" (green box) and then to the far left (pink box) and click on different playlists and find the one you want that you have saved and change it from there. Now if you just want to update the one you have then simply hit the X (red box) to remove a song and then add a new one in its place. If you see right above those tracks is a box [ ] Display on my profile - make sure you have the right player checked that you want displayed

note: loomis1031 and I are myspace friends so I saw which player he was talking about.

Thanks, Smartmom! I was strating to pull my hair out over this one! Well, I can finally change my playlists thanks to you! Woohoo, you rock!!!!