How to set a custom iphone 5c ringtone?

I have a 16gb iphone 5c and I keep having such difficulties getting a custom ringtone for my calls. I was able to get a custom text ringtone. I only have 16gb so I make it sync only songs on an "iphone" playlist which just has the one song for my text tone.

You got to convert the file to.m4r and then put it on Itunes.It will go to the Ringtones category. Then you just have to sync it to the iphone