Not necessarily. Please note that fat free is not calorie free. Many fat free foods have high carbohydrates. You can still get a lot calories from fat free foods. Look for calories not just fat content.
Both diet & exercise. Make sure you exercise at least 30 minutes a day, don't skip meals, avoid soda, juice, dairy, alcohol and fried foods. Eat a healthy well balanced diet! Also water, organic vegetable broth, green leafy vegetables, natural pickles, apples are great to fill you up so you dont feel hungry and they are very low in calories.