Is it a family? If you select it in the project do you see the Height appears in the Properties? If so, it is an Instant parameter and you can change it right there. If not, Edit Type, look for the parameter and change if you see it. If you are still not seeing the Height when editing the Type, then it is not a parameter, you need to Edit the family and modify the dimension.
Feel free to attached the family here if you want someone to look at.