Originally Answered: How can I lose weight safely and quickly?
Weight loss is actually easy, but most people are looking for short cuts. Your weight is a function of calories eaten minus calories burned in exercise. You are not very overweight, so I suspect only small changes are necessary to achieve you ideal body size.
As to food, avoid calorie-heavy and processed foods. Just say no to deserts and snacks; you'll be amazed at how much of a difference that makes.
For exercise, just make an effort to be active everyday. Walk everywhere! Take the stairs instead of an elevator, and--since you're 13--go outside and PLAY (please don't tell me you're to old for that ;-) instead of watching TV, surfing the web, or playing video games. Again, these little steps will actually result in weight loss; look at the formula at the top again--as long as you are not eating more, you will burn fat.
If you really want to be fit, find a sport/activity that you like and will love doing every week for the rest of your life. For me that is bicycling; I average about 100 miles per week throughout the year. I hate going to the gym, but cycling is something I actually enjoy doing, and I have met friends this way who I ride with every Saturday morning.
Hope this helps. I know it sounds like common sense, so get out there and try it. Don't look for a "system" to lose weight, because even if it works, eventually you will end the "system." Change your life instead!