If you are familiar with terminal usage then ffmpeg should do the job. This should do the trick:
find . -name "*.wav" -exec ffmpeg -i {} -acodec pcm_s16le {}_16.wav \;
If you would like to do sample rate conversion (for example to 44,1kHz):
find . -name "*.wav" -exec ffmpeg -i {} -acodec pcm_s16le -ar 44100 {}_16.wav \;
It will do a search in current directory for all files which have extension ending with .wav and then convert them to signed 16bit pcm with sample rate of 44,1kHz and save them with the same file name as original files only with _16 appended at the end of the name.