I'm a great decorator. No degree, but decorating is something you either got or don't got. Can't teach someone the skill.
If you are not looking to buy anything new and simply looking to re-arrange your pictures, it's very simple.
My first recommendation is to get rid of the long rectangular pic on the left. The two big pictures together won't work very well in my opinion.
Use the small picture inbetween the curtains in conjunction with the tall picture. Hang the tall pic on the center of the wall, but low. Then hang the small picture directly ABOVE that tall picture. This method is called "stacking" and will emphasize height, which will make your room appear taller/higher. However, the two pictures don't look like they go well together, but I'm recommending this assuming you simply want to work with what you have there.
My second recommendation if you want to use both large pictures still is to also use the small picture with them. Hang all three pics on the same wall, but in an "assorted" arrangement. It's difficult to explain, but what I mean is to hang the three in a off-kiltered triangle arrangement (tall pic on right, small pic on upper center, rectangular pic on lower left). The key to this is to not "align" the pictures. It will look pretty good if I can show you.