Yes, it's hidden in your user control panel.
* Click "User CP" (in the blue bar below the header ad)
* Click "Edit Options" (on the left)
* Scroll down to "Miscellaneous Options" and you'll see a menu box titled "Forum Skin". Click the little down arrow and select your forum style of choice.
* Scroll down to the bottom of the page and click "Save Changes".
You'll find lots of good stuff (e.g. displaying 50 posts per page), so look around while you're in there.