There are various different ways to increase Horsepower. The easiest is to put more efficiant air filters and better flowing exhaust. When you do, you will have to re-calibrate your injection for your changes. As delivered, in order to pass the EPA emmissions requirements, your bike is set up fairly lean. Increasing the airflow by making the changes I am discussing will compound the lean condition. Here are some products that will help you.
A better air filter is PN ZZ40502 $ 58.99
Increased flow mufflers is PN ZZ45386 $ 419.99
A fuel injection modifier is PN ZZ40999 $ 499.99