exclude a page from the menu

hi there,
i try to exclude a page from the menu. since i have a custom made theme, i cant get the “exclude” option to work and diddnt find help by searching:

the code is:

<?php 

	// content
	if ( have_posts() ) while ( have_posts() ) : the_post();
	the_content();
	endwhile;

	// list sub pages
	echo '<ul class="arrow">';
	wp_list_pages('title_li=&child_of='.get_the_id());
	echo '</ul>';
?>

where can i fit in the “exclude=123” option?

thanks for your help!!