Any good way to tune up a body for summer?

So I'm only 16, but living in California I want to have a way to get leaner before July when my friends come out to visit. They're not gay, but I don't want to stress about my body at the Beach. I've always been a little bit "husky" if you want to call it that. Never had a fat body at all, but ive always had thicker legs, hips, and calves. The problem is I don't want to lose muscle in my legs because I bike race, and go hiking alot in the summer. Any ideas to possibly slim down or build lean mass?