What Vertnut said, activity and diet change. Minimize processed carbs (white bread, white rice etc.) and replace them with food that is high in fiber (whole wheat or rye bread, whole rice, potatoes).
While counting calories isn't the most convinient way of doing things, it would help to do it for a while to get to know approximately how much you're taking in. When grocery shopping, always look at the nutritional value label for at least 5 things: calories, fat, protein, carbs and fiber. The simplified rule is that if it has a lot of calories but offers little nutritional value (protein or fiber), it isn't good for you.
Forget about diet pills, losing 50lbs out of 250lbs shouldn't be hard if you have the determination and are willing to change your diet.