I agree with the previous points made about how you're still growing. You do need to remember that. When you're about 12-13, your body goes through massive changes and sometimes extra weight is needed for those to happen. That's how it was for me.
Also, muscle does, indeed, weigh more than fat. I had a rigorous training regimine this past summer and I gained 10 pounds. But guess what? I lost 15 pounds of fat and dropped a pants size. I am overweight by traditional standards (I weigh 160lbs even and I'm pround of it), but a lot of my body composition is muscle.
When you exercise, start slow. Warm up well. Stretch for 30 seconds each body part. You should spend about 7-8 minutes stretching. Go for a run beforehand- it warms you muscles and makes them easier to stretch. Do some lightweight squats, jumping jacks, crunches, pilates, yoga, push ups, whatever, just keep yourself active. A diet will do you no good if you don't exercise. Don't lift more than 10 pounds (like Shelby said) if you haven't been trained. You can seriously hurt yourself and that is so not fun.
For food, cut out white bread and replace it with wheat. It doesn't necissarily have to be whole grain, just wheat is a good start. Don't eat pasta in excess, if you're planning on having a major workout/active day, eat a plate the night before/the morning of- it's good energy, but don't eat too much because it will only be stored for later. Try not to drink soda, or if you do at least keep it to diet/zero calorie sodas. This will help immensely. Try not to eat sweets, too. This will be hard with Hallow's Eve coming up, but try. Energy/protein bars will become your best friend. Luna Bars were the love of my life over the summer. Fruit Leather is also a really healthy, really yummy snack.
That's about all I've got. I will reccomend seeing a diatrician/nutritionist instead of taking the word of the TB as law, use us as guidelines, but see a professional if you're totally serious about losing weight. It will help a lot if you have a group of people to cheer you on, too.