How to set ringtone on iphone 5?

Ohk so i have a 30 secondes m4r file on my iTunes and iPhone 5 but i have no idea how to put it as a ringtone. Please Help!

Added (1). When I go to settings> sounds> ringtones… It doesn't let me chose songs.

Sync it to the iPhone 1st off then on the iPhone go to

Settings > Sounds > Ringtone > select the song > done.