Hi Collie650. It's good to pay attention to belly fat - generally having belly fat means you have more internal fat (visceral fat) which can lead to major health complications. You're young, so it's great that you're ready to kick this thing! Establishing good habits now will make a huge difference in the future.
To start with, being consistently active is important. Develop some kind of fitness routine and stick to it for 30 minutes a day at least 3 days a week. You may want to do more than that.
Reducing your calorie intake is another. Not overeating will help your overall efforts (and if you eat too much fat/sugar you'll be back to square one!). Good for you to monitor that sugary lemonade. One good suggestion is to add more fiber into your diet - examples are spinach, apples, corn, beans, avocado, brown rice, and whole wheat bread.
Don't forget to sleep enough, too! It's counter-intuitive, but getting enough sleep will help your weight loss efforts. If you're sleep-deprived, you're more likely to overeat the bad stuff.
Most importantly, keep that determination up! And let someone else know you're trying to lose belly fat so they can check in on your progress (and so you're more likely to keep up your mission!).