hi. So what I suggest is doing some sort of cardio 5 days a week whether it be walking running etc. I do it for about 30 min to 45 min. Do you do any sit ups or crunches??? I would do about 100 crunches after you finish your cardio. Squats and lunges work your legs and butt out. Also if you walk or run up hill that works ot your legs even better.
Eating healthy helps too..

have fun at ur pool party.
Hopefully I am of some help to you