I agree wholeheartedly with greenacrylicpaint. At my heaviest, I was running for two to three hours each day up several steep hills. I didn't lose weight. The running probably meant I could eat an extra slice of cake or a Pret sandwich without gaining weight, but the running would increase my appetite.
Also, I had a job that involved hauling heavy things around mountains for weeks every summer. I usually came back heavier because I tended to eat pizza for dinner or a large servings of pasta.
The point is, exercise is great for our health, but it's diet you want to focus on to lose weight.
I gained a huge amount of weight a few years ago and got a major wake-up call when a doctor weighed me during a check-up to prepare for a procedure. I immediately went on a diet and haven't overeaten since. I love food, but realized that the only thing that would work for me would be to give up on my food hobby. I got new hobbies. I stopped cooking at home because I can't control my portions. I only eat cake once every couple of weeks and only at cafes (because I'll eat the lot if I bake).
That may sound bleak, but it isn't. I do new activities while at home (like sewing--never thought I'd be into that, but it stops me from immediately turning to food when I'm bored). It feels so, so much better to be healthier, that food is a sacrifice I'm willing to make. And because I'm so busy, I find I don't sit around missing all the food I used to enjoy.
I still exercise insanely (weigh-lifting nearly every day, yoga twice a week, cycling at the gym--I injured my Achilles while running, probably because I was too heavy), but eased off the exercise for a couple of months when I first started the diet because it sparked my appetite. The exercise makes me feel much better, but it's the diet changes that helped me to lose weight.
You don't necessarily have to do all this. I have the kind of personality that requires focus and structure to accomplish change and maybe you don't need to be intense. What I am saying though is that you shouldn't overload yourself with feeling like you have to revolutionize your diet AND exercise regime all at once and diet is the thing to focus on to lose weight. Good luck; I really hope it works out for you.