how to put music to my phone
 

I want to put the music that I did download to my S-E W800i phone, but I am having some troubles with that.
To put it at the phone, it has to be at My Music map (or in a map at My music). I can copy my music there... but.... it has to be a MP3, otherwise my phone doesn't recognize it. And if I copy music, it changes into Mu3, which my phone doesn't recognize. How can I solve this?