Take baby steps! We're the same height (and the same age!) and I likely weighed the same as you when I started "getting healthy" (I don't know my real starting weight, but it was over 200lbs).
It took me seven years to get to this point, but I don't think I would have gotten here if I tried to do it all at once.
I started exercising before I started eating healthy when I was 16. I think at that point I dropped around 20-30 pounds to get to 200. I started eating healthier within the next few years but I didn't lose any weight. Back in May I really kicked it into gear with cutting my portions and then later on added calorie counting and here I am
Realize that you MUST change your whole life to lose weight. You cannot simply do a diet and go back to your old ways. If you are physically capable you must add exercise and couple it with healthy eating (and the right amount!) to reach your goals.