Programmatically get menu block & alter classes
borrowed from here:

add the following code in your template.php file.

&lt;?php
  function THEME_menu_tree__main_menu($variables) {
    return '&lt;ul class="nav navbar-nav navbar-right"&gt;' . $variables['tree'] . '&lt;/ul&gt;';
  }
?&gt;


this would update the &lt;ul&gt; for main menu, adjust as necessary. You can adjust further up the chain within the page.tpl.php file.