If you work on the assumption that a pound is 3500 calories, if you cut down to 1200-1500 a day and excercise efficiently for half an hour a day you should safely lose nearly 2lb a week. You don't need to make drastic changes to your diet, maybe just switching to low sugar, low fat alternatives, like weetabix and semi skimmed milk for breakfast instead of toast and butter, or vegetable soup for lunch, and trying to snack mainly on fruit and veg. That way you can still have some of the things you like. When I'm trying to lose weight I just have half portions and substitute the other half with extra portions of fruit and veg.