Alright, I'm going to be harsh! Haha(:
I don't do dressage, so I can't critique on that :P
However, I do jump. I'm a complete equitation freak!
1. It looks to me like you need to do a LOT of no stirrup work. Your leg looks loose, causing your heel to go up over the fence, instead of down. You want to have a secure
lower leg. I think of your legs being your "roots", like the roots to a tree. Without them being strong, the tree will not grow, and therefore, you won't grow as a rider. Try warming up without them, doing sit trots, posting trots, canter. Also, when your trotting around, try standing up in your saddle and 2-pointing at the trot and canter also. This always helps my legs get stronger! But, don't over do the no stirrups at first. Start small, and work your way up to eventually being able to jump without the stirrups! Trust me, doing no stirrups always always helps!
2. Your stirrups could be shorter? This could also be a reason for your heel going up. Try shortening them a hole or two, it could make a big difference.
3. In the third picture, it looked like your hands, or release, was a little too far back. You want to be able to be in 2-point position and look down with your eyes, and be able to see your thumbs. Try doing a bigger release, it will help a lot!
Videos will also help the critique, I can't tell how quiet your upper body, legs, and arms are by a picture. Get someone to video you riding, and post it here! I'd love to give you some advice, it seems like you really want to improve! http://i861.photobucket.com/albums/a...s/FAVORITE.jpg
That's a picture of my horse and I jumping. I think my release could've been a little bigger! But as for my heels, see how they're down? That's what you want to aim for!
Good luck! I bet you'll improve in no time and be a fantastic rider!=D