http://www.calculator.net/calorie-calculator.html
Calculate your caloric needs, and simply eat less than that
Calories in < calories out = weight loss
Now if you do some weight training as well, you will give your body signals that you 'need' the musles, so you're body is more inclined to burn off fat. Without weight training, your body will burn off muscle as well and you want that to happen as little as possible
Just be very vigilant and anal about how much you eat and drink.
And don't drink your calories, just stick with water, diet soda, coffee and tea (without milk and sugar).
Exercise is a non-factor compared to diet when it comes to weight loss btw