I HAVE MAJOR BOY TROUBLE!?

I'm going into highschool this September, and I really want to become more approachable to guys. However, the highschool is small, only around 400 kids. And, the kids from my grade already branded me as the "know it all nerd." I don't want that appearance of me to transfer over to highschool and make me seem un approachable to guys, because I really think i'd be nice to have a boyfriend. So how do I change my "image"?