Start making gradual substitutions to your diet, eliminating processed, refined, preserved, artificial foods from your diet. Bump up your whole grain consumption, eat a high-fiber diet with lots of fresh fruits and veggies, stay well hydrated with non-caloric beverages. Avoid artificial sweeteners which trick your body into storing fat. These are just some suggestions, not necessarily something you need to do all at once. Your body is a complex machine, and like any machine, it is only going to perform as well as the fuel you put into it. Portion control is key.