how do I disable a gui box after one has already been called?

What I am trying to figure out is how to destroy a gui box. I have multiple buttons that enable gui boxes with text. My problem is that when these buttons are pressed it doesnt destroy the gui box that was pressed before the first one.

You can’t destroy GUI boxes, rather you prevent the code which draws them from running.

if (someCondition) {
    GUI.Box (stuff);
}

–Eric