I am guessing that you want to remove the line that says <?php get_sidebar(); ?> from the template page the feeds the forum. If this page also feeds some other pages (like the blog or pages) then you will need to use some conditional code to exclude it from just the forum page.
it is more complicated than that…because i think the sidebar is determined in the css file. No “<?php get_sidebar(); ?>” appeares in the page template. Anyway the design is a purchased theme. It is called aeros theme. If you download it, see the code, and understand how i can do it,please inform me… Thanks a lot by the way for trying!! 🙂