The response that I have is quite simple—start a well-rounded major muscle group strength training program (ideally under the guidance of a certified personal trainer,) coupled with a vigorous cardiovascular training program. And follow a nutrition lifestyle that you now is healthy most of time. Don’t be nutrition fanatic. You won’t stay with if you are like most [people.
In addition to the excellent answers given by Natalie and Melina, be patient. At your young age, changes will likely be realized more quickly than in someone my age! But they will happen with patience and persistence.