[kh99]

The changes that happen as your forum is used are mostly in the database. But you say you have nothing to save anyway, so there's no reason you can't simply delete the /forums folder. If you're planning to reinstall it you might want to save the file includes/config.php so you can see how you had it configured. Also if you're going to start over, you probably want to delete the database (using phpmyadmin or other mysql tools).

One issue is what happens to users trying to go to your forums. They will just see a "page not found" error. It's possible to use .htaccess (if you have access to that) to redirect those users somewhere else.