Rejet Rancher AT

I have had my '05 Rancher AT sense new and have always thought the power was lacking. Is there a way to rejet the carb to up the preformance? I live in Iowa if that makes a difference. I have also noticed that it seems to run in a higher gear when you let off then try to get back in it. Its like it doesn't shift down until you stop. Any help will help. Thanks