Help with adding ringtones on a cell phone

I have a Samsung Slide M540 and I put in a memory card. I can add music to my phone and listen to it but for some reason I cant set them as a ring tone. Does anyone know how to on this phone?
Answer #1
Maybe there is a restriction on the phone and the music files are just too big to be used as ringtones…
Answer #2
Yea, if that’s the case, you may try it with small files. Maybe music that is running for at most 1 minute.
Answer #3
1 minutes is too long for a ringtone..When I make mine..Maximum 35 seconds…
Answer #4
Thanks, I will try that