Best way to improve upper body in 2 months?

I'm a 17 year old, 6'2", 160 pound male without much muscle at all. I'm fairly athletic in my ability but am pretty out of shape... I don't have much training in weight lifting or exercise. Since I have 2 months of summer, my goal is to get healthy, in shape, and look good for the start of my Senior Year. My main goal is to improve my arms/chest/abs... Any suggestions on how to do this? Thanks.