How can I lose weight more or less quickly?

I am a 13 year old female and I weight 137 lbs (I'm 5'5":). My friend is a little shorter than me and weighs a little less, so I figure her weight to height ratio is about the same. Anyway, we both go to a water polo summer camp every year. The camp requires a lot of exercise and being in bathing suits and we were wanting to get fit for camp so we don't get tired as easily and don't have to be embarrassed to put on a swim suit. The camp is about 4 months away so I think both of us have enough time to get into pretty good shape. We decided the basics (eat healthy, exercise more, drink water, etc.) But, we realized we don't really know a lot about what exercises to do and what to eat and still be safe, so what are some tips for getting in shape? Thank you to anyone who answers!

Try eating low calorie bars, drink water but no soda, and run at least 4 miles a day. Hope this helps

To gain one pound, you must eat 3500 more calories than you burn. To lose one pound, you must burn 3500 more calories than you eat.

To gain, eat more and burn less. To lose, burn more and eat less.

If you eat the amount of calories your body needs to maintan a normal weight, eventually you will adjust to your normal weight. The more you weigh, the faster you lose at the start, then the rate of loss declines.