How does change your Apple iPhone rigtone?

For ringtones already on your iphone: go to Settings:Sounds:Ringtone. If your looking to customize your own ringtone with any song you can pick select songs and make ringers of them on iTunes and sync those ringers with your phone. If the song your looking for isn't on iTunes go on the internet and search for "free iphone ringtone software." I use iRinger. It works well for me.