Q: How do i delete a ringtone on my phone that i baught on itunes

Hey christysu,

If I understand correctly, you want to delete a ringtone you purchased. I would recommend you read these articles, they may be able to help troubleshoot the issue. 

Delete music, movies, apps, and other content from your iPhone, iPad, or iPod touch - Apple Support

Delete a ringtone

You can't delete purchased ringtones or tones directly from your iPhone, iPad, or iPod touch. But you can delete them by syncing to a computer with iTunes. Learn how to sync your iOS device with your computer.

You can hide your purchases.

Hide and unhide purchases in iTunes or iBooks on your Mac or PC - Apple Support

Thank you for using Apple Support Communities. 
Have a good one.