Go into the Profile application and scroll all the way down to Advanced
Click the menu button and select Show Tunes - select the appropriate location (Device Memory is one)
Scroll to the appropriate ringtone, click the menu button and select Delete
I can't seem to find the Advanced application
I go into my Profiles and the norma Quiet, Off, Normal, etc show. If I go into settings and go to advanced I can find anything that deals with Tunes.