First is first, cut out any processed foods that are full of sugars and fats. LIke chips, lollies, pizza, deep fried chicken, the fish you get fro the fish n chip shop.
Second, find out what healthy foods you like to eat. Vegetables? Fruits? Nuts? Plain biscuits?
Third, make yourself a meal plan/diary. Once you've found out what you've got to cut out of your diet, and what you like and want to put into your diet, write it all down. Write in what your going to have for breakfast, lunch and dinner on everyday, and mix and match what you like. Because your still living at home, go shopping with your mum and ask her to buy you something differet so that she can cook it for you.
Fourth, exercise daily!! If you wake up 20 min before you have to get ready for school and do a quick 10 min skipping rope session, and the run around at school for atleast 10 min, and then come home and do another 10 min of running, or skipping and any other exercise you've just made up your 30 min a day! Every day you HAVE to do a MINIMUM of 30 min a day to lose as much weight as you can! You don't have to exercise everyday, but if you want to lose your weight quicker exercise atleast 6 days a week!
If you want to do more work, then go for a jog, or a brisk walk! Maybe help mum vaccum around the house and that can make up 10 min of your exercise plan! Keep motivate, and allow yourself a treat every week. But make sure its small! Have 1 piece of chocolate instead of a whole candy bar!.
Good work, and just send me a message if you want any other tips :)!!!