In the My songs page in GarageBand on your phone, tap edit and select any song (doesn't matter which one...if you have no songs just create a blank one right quick), and then tap the share button and scroll to Ringtone. If any pop-up message shows just click continue. Then tap "your ringtones" and hit edit; then you should see the red minus, which you can tap to delete the ringtone. This is the only way I've found to do it...it removes the tone from the "export ringtones" area you used to make it available as a ringtone in the first place. Doing this does indeed remove the tone from the list in Settings-Sounds. Hope this helps