What kind of exercises do I have to do to lose around 4 pounds of belly fat?

I'm going on a beach vacation in exactly 3 weeks and I was wondering what kind of exercises I should do to tone my tummy a little before I have to wear my swimsuit. I'm not fat or out of shape, but I have a little extra pudge on my belly that I want to get rid of. Do I have to do cardio, weight lifting? Is there any specific regime I should follow? I'm 15.