As is the case with standalone iPod devices, you "sync" your Apple iPhone with iTunes in order to update music, video and other content on your device. If you add or delete songs to your iTunes Library, syncing your iPhone with your computer results in the device being updated to reflect this activity. Edit the list of songs on your iPhone via iTunes.
Open iTunes. Delete any songs you want to remove from your iPhone from your iTunes Library. Add songs you want to add to your iPhone to your iTunes Library. Do this by right-clicking them individually and selecting "iTunes" from the "Open With" menu or clicking "Import Files" from the "File" menu and browsing your computer for files.
Connect your iPhone to your computer via one of its USB ports. Insert the iPhone's USB cable first into its base, then into of your computer's USB serial ports.
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Click the name of your iPhone in the iTunes sidebar. Click the "Summary" tab and click the "Sync" button to sync your iPhone with iTunes, which updates its music library to reflect what's contained within iTunes.
Disconnect the iPhone once iTunes informs you the sync has completed, a length of time that varies depending on the number of songs you add or delete. Compare your iPhone's music library to what you see in iTunes; they should now be now identical.