You don't have to practice sports, but you do need to increase your activity. Try taking a brisk walk every day. You can start slow and work up, as your energy increases. Start with, maybe, 10 minutes/day and gradually increase to at least 30 minutes/day.
You might also look into yoga; it's excellent exercise and very low impact.
Thank you for all the tips :) but it's hard to practise any sport because My activity is low
Also make sure you get plenty of exercise, in order to burn stored fat. At 16, you should be very active and activity burns fat.