How to create a sub menu for these theme?

My site is: Daily Newspaper, as you can see the problem is the subcategories Mobile and Pc tips, that are shown within the marquee.
How can i create a pop-up menu with this 2 subcategories, that will pop-up only when i hover a category with subcategories, and if it can, to pop-up UP, not DOWN.
My php code for the header navigation is

   <?php if ( has_nav_menu( 'primary-menu' ) ) {

          wp_nav_menu( array( 'menu_class' => 'sf-menu', 'theme_location' => 'primary-menu' ) );

	} else {
	?>
        <ul class="sf-menu">
            <?php $ex = get_option('swt_pages');  ?>
        	<li class="page_item <?php if(is_home()): ?>current_page_item<?php endif ?>"><a href="<?php echo get_option('home'); ?>/">Home</a></li>
        	<?php wp_list_pages("sort_column=menu_order&depth=1&exclude=$ex;&title_li=");?>
    	</ul>
   <?php } ?>
</div><!-- END PAGE MENU -->
</div>

 <div id="blogtitle">
       <h1><a href="<?php echo get_option('home'); ?>/"><img class="logo" src="<?php bloginfo('template_directory'); ?>/images/logo.png" alt="<?php bloginfo('sitename'); ?>" /></a></h1>
		<div class="description"><?php bloginfo('description'); ?></div>


 </div>


 <?php get_search_form(); ?>



 <div id="nav2"><!-- CATEGORY MENU -->
     <?php if ( has_nav_menu( 'secondary-menu' ) ) {   //checks if custom menu has been created
          wp_nav_menu( array( 'menu_class' => 'sf-menu', 'theme_location' => 'secondary-menu' ) );
	} else {// if not, old fashioned category menu will be loaded
	?>
         <ul class="sf-menu">
            <?php $cat = get_option('swt_categories');  ?>
            <li class="category_item <?php if(is_home()) { echo 'current-cat'; } ?>"><a href="<?php bloginfo('home'); ?>" id="home">Home</a></li>
        	<?php wp_list_categories("title_li=&depth=1&exclude=$cat" ); ?>
        </ul>
   <?php } ?>
 </div><!-- END CATEGORY MENU -->

Code (markup):

My style css you can find it at: http://www.imediazone.net/wp-content/themes/MasterclassMagazine/style.css

 

This is complicated, because you will need to create the php code from scratch for the child categories or submenu.

 

you can put sub categories in same place.....and it looks goods in the same place than pop up at up....increase/dercrease 'z-index"of CSS of the submenu defenitely will solve the problem...