How can I lose 15-20 pounds?

I would like to lose about 15-20 pounds. I'm not fat, but I gained 13 pounds over the last year and only grown half an inch, which is really unbalanced. I'm pretty sure that I carry most of the weight in my lower body. ( and thighs) What can I do to lose this? I'm not asking in like one month. But maybe by Christmas, I would like to have reached my goal. Exercises, food ideas, motivations, and any other tips you have for me would be greatly appreciated. (: