Help with the Menu in Grey Matter theme please

Hi everyone. Maybe somebody here can help me with something.
I like the Grey Matter theme. One snag with it, it automatically adds every page to the top right hand menu.
I am hoping for some help with how to exclude certain pages from this menu, such as thank-you pages.
I am not a coder. Looking at the theme, I think the menu is controlled in here, within header.php

<!-- Page Navigation -->
<div id="blackband_top_right">
<h2>
<ul id="dropmenu">
<li class="page_item<?php if (is_home()) {echo ' current_page_item';} ?>"><a href="<?php echo get_settings('home'); ?>" title="<?php bloginfo('name'); ?>"><?php _e('Home','grey_matter'); ?></a></li>
<?php wp_list_pages('sort_column=menu_order&title_li='); ?>
</ul>
</h2>
</div>

Experimenting, i tried changing that red line to
wp_list_pages('exclude=40', 'sort_column=menu_order&title_li=')
40 is the page id that i want to exclude in this example.
Didnt work very well - yes it excluded my page, but all the menu items became drop-down items below a single entry called 'Pages', instead of being listed along the top.
Is this easy to do somehow?
Thanks in advance
Brian