Scott gave a quick overview of how to find the voices and change them. If you'd like a more detailed explanation with pictures, check out the lessons on adjusting styles at psrtutorial.com. Here is a direct link:
http://psrtutorial.com/Lessons/L_Personalizing/LP_AdjStyles/lp_adjstyles.html

There are individual lessons on the Balance Control, the Mixing Console, setting the Master EQ, Fine Tuning style settings, and creating One-Touch Settings.