Right now you should stick to the height your jumping and develop more strength in your horse and in yourself. After that I recommend every time you jump raise it one hole on the standard and talk with you trainer about exercises.
It will come over time- you shouldn't jump a youngish horse too high or you'll break it. Develop balance, impulsion, and experience first. Jumping higher isn't better!
right, you can't necessarily teach a horse to jump higher than what it can, it's like a human athlete..everyone is different and has a different potential
The height is nothing you teach it is something that comes with development, strength and experience.