Playing in the high range of the trumpet is difficult for beginners only because of the bad habits we acquire early on in trumpet study.  Playing high notes does not require a significant amount more of lip muscles, but instead requires a specifically focused way of using the lips together with massive amounts of unhindered air coming directly to the lips.  It takes time to train the lips and air in the right way, but the most important things to focus on are

1) keeping the embouchere consistent and balanced, especially in the size of the air opening (feng kou)

2) opening the throat so that air flows very freely through, and when these two are mastered,

3) using the tongue to more accurately control the exact air pressure in the mouth cavity, which gives accurate control over the different notes in the high and extra-high register of the horn.