I am very fat around the belly and chest
I am only 15yrs old but aldready 98 kilos
I really want to decrease my weight I'm desperate

1. Eat whole fruit and vegetables, including beans--LOTS.

2. Eat fewer grains (bread, pasta, cereal) and eat whole grains when you do.

3. Give up soft drinks and juices, and drink water instead.

4. Take a half hour walk every day rain or shine. You can walk in the rain. You won't melt. :)
If you can run for part of that walk, do. But the main thing is the walk. Walk briskly. Don't give up if nothing happens right away. Be patient and persistent. You can do this. :)

4. Because you are probably still growing, make sure to get plenty of calcium. You can drink 1% milk and you should eat leafy green vegetables (which have calcium). But avoid high fat foods such as whole milk, ice cream, cheese, and butter. You can have very small portions of these every other day or so. But they should be like a square of chocolate--a treat, not a significant part of your diet. Ban pizza for 6 months...

5. No fast foods or similar prepared foods.

(Don't drink soft drinks--not even diet ones!)

Come back here and tell us how you are doing. You are likely to get lots of advice here. Some good some bad. I read a lot of scientific papers about human diet, not long ago, as part of my work. This is my best advice.

It is really hard to resist the kinds of foods that are making you fat, because they are designed to make you want them. But they are really bad for your health, as you can see. Think of them as like addictive and illegal drugs if that helps you.