[BSMedia]

You can rename the forums index.php to something like forums.php (There is a setting in the admin panel that needs changed to)

Then upload all the wordpress files to your web root.

Edit:

After visiting your site you either have either a redirect on your index page, or an edit to your .htaccess that is redirecting people to forum.php first.

So basically all you need to do is upload wordpress in to your root, and remove whatever the redirect is.