Diet and exercise - boring but proven.
Start by not even changing your diet. Just eat less. Eat sensibly sized single portions.
Then when you've mastered that, begin to increase the amount of physical activity you do. Use the stairs, not the lift. Ride a bicycle to work. The trick is to find a physical activity you enjoy - it makes it much easier to keep it up in the long term.
Having mastered eating less and exercising more, your next task is to improve the quality of the food you eat. Plenty of vegetables and fruit, rice, oats, wholegrain breads, fish, chicken, cut back on red meat.
Increasing your metablism through these three steps is the name of the game. You'll look better, feel great, and it'll do wonders for your private life.