Everyone has a fear of something, some more irrational than others, I have a couple irrational fears and have had many problems getting over them. My best advice is to slowly (literally) present yourself with that situation. So I would go to something that is not very high off the ground and start yourself off slowly from there and gradually get higher and higher but only as much as you can take. You can't force yourself to like them but you can gradually get yourself used to them.
The experts say to face any unnatural fear head on. That's difficult though. I would just try to go a little higher each time I would be faced with the obstacle. Go nice and slow and increase the exercise every time. But to force yourself to be in a very high place suddenly, seems too drastic.
Fear of heights, to a certain extent, isn't abnormal. In fact, as long as it's not too extreme, it's perfectly natural, since fear of heights would lessen a person's chance of falling and dying. It's a natural instinct that aids in survival.
Everyone is afraid of heights! Don't let anyone tell you differently. We are animals (yes, just like other land mammals that we love) and we are grounded by gravity. It's what we know. When placed above the ground our equilibrium feels twirled, and balance becomes surreal. Think forward thoughts and visually SEE yourself on the other side. If you can't see yourself on the other side, find a place IN FRONT of you that you can make a goal to meet. If you're going directly up and then down, (elevator style) think about the things you will do once you get to the top, or in reverse, how wonderful it'll be to run those darn errands you've been meaning to do! Don't worry so much. It's good you're going UP! Good upwards thoughts! Breathe! It's O.k. to be afraid. Peace.