Using your Hornit Kids Helmet Shark is easy. First, adjust the head adjuster to fit your child's head size properly. Make sure it's snug but not too tight. The small size is for heads 48 - 53cm, and the medium size is for 54 - 58cm. To turn on the LED, just switch it to one of the 3 modes. Remember to replace the 2x AG3 cell batteries when they run out. For maintenance, clean the helmet with a mild soap and water solution. Don't use harsh chemicals as they might damage the helmet. Keep it in a cool, dry place when not in use. Always check the helmet for any signs of damage before each use. If it gets damaged, replace it right away to ensure your child's safety.