Try using myfitnesspal or a similar app, I'm sure there are plenty about. It helped me to track what I was eating and where I was going wrong, in time you start to know what are good meals and adjust your eating accordingly. Reading back my advice above, it seems a bit blunt, but I was pushing on for 17 stone a few years back and sorted myself out by first of all learning what I was eating, improving that and then gradually becoming more active, as above it may be better to walk at first depending what fitness level you're at. The first run I went on, I was fucked after about 1/2km and my feet and legs were numb at about 1km, but I kept at it and easily and regularly run between 10km and 20km with no problems and am now generally between 10 1/2 and 11 stone.