If your phone supports external card, the easier way is to put the new ring tone in the external card and plug it into the phone.
Using the setting menu, change the ringer section and choose the ring tone you would like.
If your phone does not support external card (like my CDM-9900), you can still upload the new ringtone to your phone by sending yourself an e-mail with attachement. To do so, you send an e-mail with the ringer attachement to
yournumber@vzwpix.com. After you receive the message, go to Option and Save the message as Ringer. Now, the ringtone is in your media gallery or My Music section.
Using the setting menu, change the ringer setting and choose the ringtone you would like.
(Receiving this type of message will cost you $0.25 per message. Still cheaper than purchasing it from Verizon)