In all honesty, your jumping position is a little bit scary. You have no base of support and your center of gravity is no where near that of your horse in most of your pics. A strong gust of wind could currently knock you over right now.
1st pic: You have completely lost your lower leg. You want your stirrup leather to be perpendicular to the ground, with all your weight sunk down into your heel (which will be the lowest point on your body). As you can see, your leg is pretty much in a different zip code than the rest of you.
So that's the first thing to fix. Next on the list is your seat. Your crotch should be centered over the seat of the saddle, not over the pommel. Additionally, there is WAY too much space between your butt and the saddle. That much air room, you aren't secure. Your center of gravity is not matched up with that of your horse, you are weighting down his front end, making his job a lot harder (and making your job a lot harder too, it's harder to stay on and ride when you're not in balance with your horse).
Your back is pretty good, not perfect (could be a bit flatter, and your shoulders back a bit more), but it's decent. For your release, your fingers should be closed on the reins and your hands should be pressed into the crest, not the mane. Also, I think you're looking for the turn a bit early, ride your horse straight, then turn, at least at this stage in your riding.
Pic 2: Here, you got left behind. Once again, your lower leg has flown back and due to that the rest of your position has fallen apart. Your center of gravity is behind your horse's, making it harder for him to jump. Additionally, you haven't released enough and you are catching him in the mouth. You are too far back in the saddle, and your shoulder's are up by your ears. You seem very tense and nervous.
Pic 3: This picture is the best for seeing what exactly is going wrong. Like all the other pics, it all comes back to your lower leg and heel. Your lower leg has flown back, you have flung yourself over the jump. You are so far ahead of his center of gravity that he's having trouble jumping (note the knees). Your base is so distanced from your horse that you are pretty much detached and your release is up by his ears.
Pic 4: This is probably the best pic (maybe it's just the angle). Your heel is bad, but not 'lets fly away in the wind' bad. But, once again, you are jumping way ahead of your horse.
My recommendation is to take a step back and get yourself solid on the ground first. Lots and lots of two point on the flat and over poles and low cross rails.
Don't think of it as taking a step back, think of it as an investment. The more time you spend on the basics now, the better you'll be in the long run.