All the information these guys are giving you are really good. I used to be a fat kid. It took a long time and dedication. Don't get any of this information wrong, you don't have to stop eating the "fun" stuff to get into better shape. You simply have to use that food as treats. All the stuff that most people dread eating, guess what their good stuff. Veggies, unprocessed foods, lean meats, water, and the list goes on. I started simple. First change I made in my life was what I drank. I stopped drinking everything else and the only liquid to touch my mouth was water. No milk, no juice, no soda, nothing with any color, flavor or taste. That alone made me dropped 10 lbs maybe more. Then I slowly started taking out the things that I knew were treats, candy, ice creams, deserts all that stuff. Again I dropped another 10lbs or more.
After all that I was still big. I know in this time and age it's hard to cook every day. Not all parents use fresh foods and processed foods are much easier and tastier to eat. So as a young man I had two options starve which would have been the worst thing in the world or change the way I ate. My parents always told me to eat the whole plate, blah blah blah you won’t grow. Well I was grown. I wasn't tall, but I surely was wide. I looked in the internet and I found something that worked for me. PORTIONS. In time I learned not to eat two, three, four servings of anything and stick to the right amount for my body. Most dieticians will tell you about the fist rule. Veggies cooked in water, HAVE AT IT! Meats, only one piece the size of your fist. Carbs, half the size of your fist. That method helped me lose another big chunk of weight.
The last phase this trip I been on is the part of learning when to eat what. This took allot of research and talking to other athletes, doctors, internet, books, etc. Learning what times to eat what foods has allot to do with how the body functions and what you plan to do on that particular day. Simply put, you want to eat high energy food early in the day so your body has time to burn it while you’re doing your daily activates. Heavy meats, dark meat no later than 2-3pm because those take a while for your body to process. Night time you want to lean off the carbs because you're going to sleep. There is no need to load up on those. However, veggies, leafs, some white meat like chicken breast or baked fish is also great to help your muscles rebuild and replenish.
Best advice I can give you is take your time.
Be consistent. Thing will not happen overnight so be patient.
Start slow, take one bad item out and replace it with something good. Example: Ice Cream between meals, replace with a fruit.
And continue in your BJJ Journey. It is a great form of exercise, self-defense and an awesome way of life.
I believe in you buddy. You can do anything once you put your mind to it.
P.S. Oh, and about treats. Keep those far and few.