Nokia

I recently bought the 6133 and want to convert mp3s to ringtones. I knew buying the phone that native mp3s can't be used as a ringtone but I read somewhere there are programs available to convert. My only 'puter with Bluetooth to send the files to the phone is my Mac. I'm having trouble finding a decent program. Does anyone have any suggestions? I have a PC also and can transfer a file to the Mac if needed but really hate working on that dinosaur.

Thank you anyone who can give me a little direction!
😁