I was not a overweight growing up, but after college, I noticed that I started to put on a lot more weight and growing a tire around the midsection became easier and easier as I got older, especially when I regularly consumed beer/wine/hard liquor.
I went to work in Japan for a few years and I got around to caring about my diet, partly due to necessity because eating more "western" foods in Asia usually cost more. It's been several years since then I'm happy to say that I figured out how to slim down and fight fat for my body. Maybe what works for me may work for you.
1. Avoid all forms of processed foods. This essentially means eating out very rarely, because restaurants tend to use the cheapest ingredients they can find. Processed sugars and oils are really hard for the body to burn, and even if you are active, if you're putting a lot of processed foods into your system, the best you can hope to achieve is probably just staying at your current weight.
2. Reduce sugar intake (this includes bread and all forms of alcohol), and increase fiber intake. Eat oatmeal, eat veggies, eat fruit.
3. Learn to drink WATER. Not soda, not juice, not energy drinks, not gatorade, get back to the most important liquid there is, water.
4. Be active to increase your metabolism. Work out, use weights so you can build more muscle, do workouts in the morning so your metabolism is "turned on" for more hours in the day.
5. Eat smaller meals more frequently. 5 or 6 meals a day, with portions about half of what you'd normally eat if you were eating 3 meals a day.
I think the hardest thing is definitely (1).
The reality of food in America is that so much of it is fast food and processed food, that when a person actually tries to eat healthier, unprocessed food, they will find it very inconvenient. Cooking oatmeal takes at least 10 minutes, eating more fiber means less sugar, less salt, and less fat and oils in your food too, and this can really take some getting used to. What do you do when you are with other people and they want to get pizza? Or worse yet, you just feel lazy and want to buy fast food?
I hope some of my ideas help give you a starting point. Good luck, I hope you find a healthier version of yourself soon.