No probs
1. Download & Install
Astro File Manager from the market
2. Open hit
3. Hit the Search Button on your handset
4. In the Page that appears, type the name of the ringtone you want to delete, press the magnifying glass on screen.
5. The file should appear on the screen, long press it and select open folder/directory, select that
6. Long press the file again in the new window and press delete.
All make sense? If not, just follow the instructions and tell me where you get stuck.