How do I add ringtone...Verizon&AT&T don't know

Source: forums.macrumors.com --- Saturday, July 16, 2016
I have a ring tone I downloaded and put in itunes (using my mac)...I want it to be my ring tone on Apple iPhone C Went to Verizon store and AT&T....was told they had no clue how to do and there is NO Apple store anywhere near me. Can any tell me a simple way to accomplish this...please dont leave out any steps. Thanks ...

from Apple http://ift.tt/29LTZR2