More room by the text area

I have a lot of categories in my blog. When I go to post a post. It has a scroll bar going up and down. I already went into the style sheet and lengthened the div that is holding the categories. Now it is going past the part that it is in, the “wrap”. It is sorta hard for me to explain.

I am trying to make the area below the text box that you type the post in larger. I don’t know what file that textarea box is in, I tried post.php and admin functions.php

THanks.