I am want to know how to unlock a ringtone on a sprint palm centro?

What do you mean by "unlock"? If you're looking for free ringtones, I would try Myxer - Download Ringtones and More (http://www.myxer.com/)

Plenty of free ones. If you want to make your own ringtones and load them on your phone, I would recommend a product called "Ringo" from Handango. It makes it easy to load your own tones on from your computer and set them for different functions. You can use an audio editing program (I use CoolEditPro) to cut your tones or mix them.