how to convert an mp3 to a ringtone? verizon; network/ samsung sway; phone?

ok so i have this 8 second mp3 that ive tried to turn into a ringtone using an online converter www.makeyourownringtone.com then plug my phone in to a usb port and place the download new mp3 into “my ringtones (micro sd card) but when i go to move the file to the phone from the card it puts it in my music. now im trying to find a converter to make the mp3 an midi or mmf but i cant find one thats free