Changing audio bit rate after recording

I'm recording audio files at a bit rate of 44.1khz. I like having high quality audio for playback purposes. However, when I want to export via text or email, the audio files fail to export because they're larger than 15MB (usually for audio files +3mins). Is there a way to reduce the bit rate only when I want to export? I've seen the following tutorial, but I'd rather keep my files as m4a rather than converting to aac: http://ift.tt/15EzJ0C.