Whats the space between shelves? About 18 inches or so?
They are adjustable, but it is limited because you absolutely must have a shelf right in the middle because it holds the top and bottom pieces together. Of course, you are generally going to put one on the top and one on the bottom, so you can really only adjust the other 2 shelves.
This is a great deal for some good shelves. I have some and while the particleboard does sag a bit after a while, it still holds what I need it to hold without breaking, so it is not bad enough that I have replaced it. If you want to hold something really heavy right in the middle of the shelf it might be a problem, but if the weight is pretty well distributed it works.