Theming menù

Hi to all, I've a lot of subtheme each one with a custom menù.
the primary links menù structure was made by ul class="menu nav navbar-nav" (bootstrap dropdown menu).
Any new menu has this structure:

<div class="region region-mainmenu">
	<section id="block-menu-menu-main-biblioteca" class="block block-menu clearfix">
		<ul class="menu nav">
			<li class="first leaf"><a title="" class="nolink">First</a></li>
			<li class="last leaf"><a title="" class="nolink">Second</a></li>
		</ul>
	</section> 
</div>

How to have the same structure (bootstrap dropdown menu) for each menus?
Thanks a lot
Stefano