Lucy if you want to lose a few pounds the best way to do it is to do fun exercises that are really cardio intense! I like to do kickboxing, there is a studio near my house, or you can do things like ZUMBA and other fun workout classes. The point is to just do it, no need to plan it out of get your diet food first. Just exercise then you can plan after you've started.
I was really thin in my teen years untill I suddenly gained 25 pounds, I lost it by the time I was 19. But now I always watch what I eat and I've added lifting heavy weights in with my exersice routine so I look more tonned. It's definitely a lifestyle!