ringtone not showing in tones

I was trying to get a clip of a song as a ringtone for free by changing it from an mp3 file to a ringtone (I used the article linked at the bottom), but when I converted it from m4a to m4r, it wouldn't show up under tones. I'm currently using the most recent version of itunes. Does anyone know how to fix this or what the problem might be? Anything is appreciated.