Convert M4a audio files to MP3 format

First you must install the necessary programs for this process.
Open the folder containing the M4a file, right click in the folder and open in terminal window. Enter the following into your trerminal window.

sudo apt-get install faad
sudo apt-get install lame
sudo apt-get update

Enter your password when requested (will be hidden)

Now to convert one single M4a file to MP3:

Enter the following into your terminal window:

faad "yourFileName".m4a "yourFileName".wav

lame "yourFileName".wav "yourFileName".mp3

To clean up the left over .wav files from your system enter the following into your terminal window:

rm "yourFileName".wav

You should now have a MP3 file with the same name,