1. download 'switch sound file converter' free
2. click on add folder at the top and choose the songs u want to convert
3. click on browse to find a folder for your converted songs to be put into
4. change the output format to .mp3
5. click on encoder options
6. click on constant bitrate and also high quality encoding and change the bitrate to 24 (the higher the bitrate the higher the quality but bigger the file, i choose 24 because the quality fine and the file is pretty small)
7. change the channel encoding mode to mono and also click on include CRC to Detect Errors. then click ok
8. click convert in the bottom right hand corner and your files will convert.