I went to the sprint store this weekend with my Intercept phone. I was told that there was NO WAY to delete the ringers. Nor was I able to asign ringers to my contacts. I had downloaded 8 ringtones. So, they reset my phone, saved and reinstalled my contacts. This erased the ring tones from my phone. They said this was the ONLY way. However, this also wiped out my calendar.
You can assign ringtones to contacts so sprint store was incorrect on that but still searching how to delete duplicate ringtones. I'm determined to figure it out so I'm sure I'll do it somehow.
Ok, I have found a solution, though not a great one. Of course if you are using a ringtone from a song that you put on the mp3 portion of your phone it is easily removed. For those of you that download from Myxer or other such site it is protected by the DRM. There is a way to delete this content, however you have to delete ALL of this content. So if you have multiple downloaded ringtones, backgrounds, etc., it will all be erased and you have to download it again. Here are the steps: Go to Settings, Applications, Manage Apps, hit the Menu button, Filter, All, DRM Protected Content Storage, Clear data. Again, think before you do this as you may not want to lose everything or at least have it backed up elsewhere.