Diet is key. While it is possible to reduce your weight by increasing the amount of exercise you do, it often doesn’t stay off because you need to continue that exercise regime to keep it off. As the saying goes: you cannot outrun a bad diet.
Once you have your diet under control, it is also useful to consider the guidelines for physical activity that I have referenced before and perhaps done in combination with a monthly 45 minute physical fitness test.
To put it another way, if you worked your way up to doing a running 10 miles every week, did it for a year and kept your diet the same, it would burn ~700-1500 calories a week, which would result in weight loss of between 10-20 pounds a year.