How to convert M4A to MP3?

Well some M4A files have various locks on them for copyright reasons, so if it's locked, you're pretty much S.O.L. Yes there are ways around it, but none of them are easy. If there are no locks on the file, then try zamzar.com it's an online file conversion site, I use it all the time it works great. Just select the file on your computer, select MP3 from the drop down menu, type in your email address, and click "Convert" they then send you a link to download it from within minutes.

you can use this iMoviesoft Audio Converter
it can extract audio from video files including MPEG, MP4, M4V, MPG, MPEG2, WMV, ASF, MKV, MPV, AVI, 3GP, 3G2, FLV, MOD, TOD, such as converting MP4 to MP3, FLV to WMA, MKV to AAC,M4A to MP3, etc.

click on its propities and customize the file type quick and simple

Aviosoft Video Converter extracts your favorite music from MPEG, HD, DVD, QuickTime, DAT, RM, RMVB, AVI, WMV, ASF, MPG, MPE, MP4, MOV, VOB… and converts to MP3, MP2, AAC, AC3, M4A; converts any audio files to MP3, M4A, AAC, AC3, MP2. Aviosoft Video Converter features converting video files to common video AVI, ASF, MOV, MP4, WMV, 3GP; to HD video AVI, MP4, MPG, MKV, TS, WMV, MOV; to Apple, Archos, BlackBerry, HTC, Nokia, Sony, Mobile Phone. Additionally, Aviosoft Video Converter offers edit tools to clip/crop/merge/add watermark and subtitle, makes pictures slideshow with title, credits, background music, effect; downloads movies from YouTube and Yahoo. Then slideshows and downloaded movies convert for playback!