How can i decrease my weight and become very fast in running?

Weight loss: Start strict diet low fat low carbohydrate and put a program of exercise gradually increase your excercse.

Training: Increase your distance and speed in increments, not all at once. I would first go to a running track, if possible, and walk and run laps. Slowly increase the number of laps you run, then the speed over time. Stamina builds very quickly, but you also lose it just as fast if you are not motivated and stick to your goals and program.