That's a simple one. First start the midi file. Then press the (mixer) button. This gives you access to all 16 tracks. Then use the (left) and (right) curser to select idividual tracks. Example: say you selected track 3, and there is a guitar voice assigned to it. Just dial in the number of another voice and that track will change. You can then use the (down) cursor to change other parameters to the same track such as reverb, pan, volume, octave, ect. You can do this with all the tracks. Unfourtunately there is no way to save those changes (or at least I haven't figured it out yet). Also a downside is that you cannot make changes until you press the start button. If you make all your changes prior to that and then start the midi file it will automatically go back to the default settings. Hope this helped.
GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.