How to lose 40 pounds in 5 months?

I currently weigh 170 pounds and would like to weigh from 130 through 145. My current measurements are 38-32-38. Most of my weight is in my lower body, I have a large hips and butt and would like to lose fat off of my thighs and stomach. How often should I treat myself with a soda or something of that sort?Please give me some workouts that will help me.