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Ringtones have to be purchases on the iPhone itself, unless you created a custom ringtone in Garageband.
I've included some information below for you for both scenarios.
Here is a quick tutorial on how to purchase and assign Ringtones:
The iPhone User Guide for iOS 7 explains how to purchase from the iTunes Store (pg. 99), and how to assign ringtones to your contacts on page 47.
Choose Send Ringtone to iTunes from the Share menu.
In iTunes, use the Ringtones pane to select the ringtones you want to sync to iPhone.