Disklavier

This may be a basic question, but nonetheless I need help. I have 
downloaded .mid files from the Internet but when I play them on the 
Disklavier all I hear is the sound from the speakers.  The piano does 
not play.  I realize the piano parts are not on the right tracks.  Is 
there software available which will allow me to manipulate the .mid 
files so that the piano will play the .mid file?  Thank you.

William