Convert to wav, open windows sound record, set desired length, go to edit and press "delete everything after this position", save, and convert back to Mp3. Finally upload to your phone.
Go google "Audacity" and download it. Its a free and easy program for editing sound. Listen to the parts of the song you want, then to delete the rest you dont want highlight it and hit the delete button. click file save as-->Mp3 or export as --> MP3 and then you have a ringtone.