Digital Media Converter cannot remove the audio from a video file. In Digital Media Converter Pro, to create silent video files click Tools >> Effects >> Change Volume Level, and change the volume level to 0.
We have published an article on creating smaller files, which you can read here:
https://www.deskshare.com/resources/articles/dmcpro_ReduceFileSize.aspx
WMV and MP4 formats can both produce very small files, but the size depends on the settings you select.