I've been playing trombone for a year and a half and we're doing some songs with pretty high notes (for me) in it. Its High E flat and High D on the second and third ledger line. I can play the notes but they sound like a squeaky airhorn. I'm either playing too high or not high enough, can you guys help?

The most important thing to remember when you're working on high notes is to stay relaxed.
There are three aspects of your playing that need to change to get higher:
1. Air speed needs to get faster
2. Aperture (the circle made in the center of your lips when you buzz) needs to be more narrow. Make sure it's still a circular shape and not flat or tight. Think of saying ooooo
3. Air direction needs to be pointed down to the bottom of your mouthpiece.
See below
https://youtu.be/3fZCciB2DVM

A great exercise is to play a Bb on top of the staff with a great tone in 5th position, then glissando up to first position. If done right you will hit the D above that in 1st. Strive to maintain the same tone quality as you gliss up. You will have to blow faster as you go up as well. Play a high C in 6th position and gliss up to 3rd position to get to the high Eb. Hope this helps

I agree. Relaxed is the key. It's the force of airflow that changes as well embouchure position. I can regularly hit double high Eb. Even when tired after a long practice.