I have a ringtone I purchased on the Internet. I managed to get it in my iTunes library and it's on my iMac and my iPhone under "My Music" but I can't figure out how to get it on my phone as a ringtone. I know it's possible because I did it once before, but I am having a "senior moment" because I can't remember how I did it. Help please. I have an iPhone 5 S Thanks.