Open up your favourite audio editing program, on any of your PC/Mac/Linux machine.
Select the song/audio file that you want to use as a ringtone.
Edit, cut, stitch, enhance, fade-in/fade-out whatever is your heart desire.
Save it as a 16bit PCM wav file.
Copy it onto your external SD card. Open it with your phone Music Player, then from the Option Menu (within the Music Player) select ...Set as... than set it as a ringtone. Piece of cake.
NB. you can organise your ringtones into folders BEFORE set them as ringtones, but if you re-arranging your files/directories on your external SD card and/or remove those files, the ringtones are gone too.
Enjoy!