To set up an individual ringtone on an iPhone, click Contacts on the home screen of the iPhone. Select the appropriate contact for the ringtone, and tap Ringtone. Then select the ringtone that plays when this contact calls.
All iPhones are sold with a variety of ringtones installed, but ringtones can also be purchased through the Apple iTunes online store with an Apple ID. To purchase a new ringtone, click on the iTunes store app on the iPhone. Select Tones, or, depending on the iPhone version, select More and then Tones. Scroll through the available tones and select the tone to purchase. Once the tone is bought, a dialog box appears that allows the tone to be set to a contact or as the new default text tone or ringtone.
Ringtones can also be purchased using an iPod or iPad synced to the iTunes library. These tones can be accessed on the iPhone by connecting it to the computer and syncing it to the iTunes library. Open Settings on the iPhone and select Sounds.
To change the ringtone for a contact, click Contacts on the home screen and tap the contact to change. Click Ringtones and choose the new ringtone for this contact.