Create drop down Menus in Nav Bar

Hi, I have a theme which I would like to alter. My home Page has headings in the Nav Bar but would like to make them drop down menus.

I have added this to the functions.php page

add_theme_support( ‘menus’ );

In the header page I currently have this

<?php if ( function_exists(‘wp_nav_menu’) )
wp_nav_menu( array( ‘title_li’ => ”, ‘depth’ => 4, ‘container_class’ => ‘menu’ ) ); }
else {?>
<ul class=”menu”><?php wp_list_pages(‘title_li=&depth=4’); ?>
<?php } ?>
</div>

I think I need to add the following code

<?php wp_nav_menu( array( ‘sort_column’ => ‘menu_order’, ‘container_class’ => ‘menu-header’ ) ); ?>

Do I just replace the top code with the bottom code or is there something else I need to do?

Thanks