Please tell me some good ways to help a teenager jump higher, and make his shrank thinner?

Hi, my little brother is 16 now. He plays basketball. He wants to jump higher. His coach thinks his shrank is a little bit fat for a basketball player. Do you have any good training ideas for him to jump higher, or maybe let his tendon grow longer, or his shrank become thinner? Will these techniques disturb his body growth?
l am waiting for your answers. Thanks a lot.