[ubuntu-uk] How to delete all .m4a files from music library

[Mac]

I've got a mixture of .flac and .m4a files of the same music scattered 
through the multiple sub directories in ~/music.  I want to delete all 
the .m4a files from which ever subdirectory they happen to be in, 
leaving the .flac files in their current directories.  (It would be nice 
to delete any directories that have become empty because they only had 
.m4a files in them - but that would be a bonus!)

I'd be grateful for advice about how to do this 'selective recursive 
delete' - I can't work out a terminal command with this effect.

Sorry if this is dead obvious - I can't see how to do it.

TIA

Mac