Question about custom menus (Teknohippy solution)

Hi there,
I was reading post http://wordpress.org/support/topic/custom-menus-on-different-pages?replies=23 about custom menus for themes.

I am using clean retina and the code is not in header.php
I have found the coded in header-extensions.php but the code is different:

<?php

			if ( has_nav_menu( 'primary' ) ) { 

				$args = array(

					'theme_location'    => 'primary',

					'container'         => '',

					'items_wrap'        => '<ul class="root">%3$s</ul>' 

				);

				echo '<nav id="access" class="clearfix">';

					wp_nav_menu( $args );

				echo '</nav><!-- #access -->';

			}

			else {

				echo '<nav id="access" class="clearfix">';

					wp_page_menu( array( 'menu_class'  => 'root' ) );

				echo '</nav><!-- #access -->';

			}

		?>

How do I apply your code in this instance please? I tried, but completely messed up the whole site!!

Many thanks
Alex