Hello Geronimo and welcome to the forum.
Although your current weight doesn’t cause particular concern, it’s good that you recognise that you need to change the unhealthy eating habits that may have led to your recent accumulation.
However, in your quest to shed any excess, bear in mind that as a teenager, your body requires a certain amount of daily calories as it’s still developing. Whilst introducing a daily calorie deficit will assist in weight reduction, don’t consider introducing an excessive deficit.
To gain a clearer idea of who many calories you should be consuming, that’ll provide your body with sufficient energy while running a deficit, obtain both your BMR and TDEE using the figure between the two as your daily calorie deficit.
As for how you become healthier, there are many things you can do. By reducing intake of refined carbohydrate (cakes/sweets/pastries), replacing simple carbs with complex alternatives, while ensuring that protein is obtained from lean sources, you’ll begin to make changes. Additionally, reduced consumption of saturated animal fat and increased consumption of vegetables will also help to improve your overall health.
Concerning exercise, provided you’re participating in activity that raises your heart rate to a level that breaks a sweat, you’ll be improving your level of fitness. As your level of fitness increases, you’ll find that you’re able to sustain the activity (whatever that may be) for longer.
While you appreciate that changes need to be made, don’t lose sight of the fact that your body is still developing, Geronimo. As such, seek to implement changes gradually, figuring what works best for you. By adopting a measured approach, you’re less likely to be left feeling overwhelmed.
I wish you all the very best, Geronimo. Remember, though, Rome wasn’t built in a day.