AMR sounds are recorded usually by some mobile phones. AMR files can be converted to .mp3 sound files easily. Some dedicated multimedia or audio converters offer the possibility of conversion between the AMR and MP3 audio formats. But keep in mind that AMR is a format optimized for speech, not music. You can pick from any of the choices listed below, all these programs should be capable of amr to mp3 conversion.
We suggest you Freemake audio converter on Windows or Miksoft Mobile Media Converter on Mac.
You could use either a dedicated media converter program, or a general purpose audio editor like for example Audacity.