So I just bought the Roland GW-7

I have an external sequencer/sampler (MPC 2000xl) feeding midi sequences to the Roland GW-7

I need to set the tones (sounds) on my 16 channels in my Roland GW-7. How do I do that in the keyboard?

Basically, how do I go into the GW-7 to set what sound comes out of Track1, Track 2, Track 3 etc all the way to 16