I want to save a m4a file to a wav file

For what its worth iTunes can do this.

A .m4a file is an audio file containing either Lossey AAC or Apple Lossless audio. It does not make a lot of sense to convert AAC to WAV since this will not improve the audio quality and mike make it actually very slightly worse but Apple Lossless and WAV would have exactly the same audio quality since both are lossless formats.

Why do you need WAV since it would be no better audio quality? You should be aware that Windows 10 fully supports both AAC and Apple Lossless as standard in Windows Media Player.

Note: The meta-tag support in WAV is very poor, the tagging support in .m4a is excellent. Again Windows 10 fully supports this as well.

this is my "Swiss army knife" for audio

http://www.audacityteam.org/