[Theme Horse Support Team]

Hi aaron1,

This is an example how to unhook page 404.php and use your own content.

unhook functions

// Unhook default Thematic functions
function unhook_thematic_functions() {
    // Don't forget the position number if the original function has one

remove_action( 'attitude_404_content', 'attitude_display_404_page_content', 10 );

}
add_action('init','unhook_thematic_functions'); // removes the header content by using hook attitude_header

add_action( 'attitude_404_content', 'attitude_child_display_404_page_content', 10 );
/**
 * function to show the footer info, copyright information
 */
 
 
function attitude_child_display_404_page_content() {      ?>   
<div id="content">
		<header class="entry-header">
			<h1 class="entry-title"><?php _e( 'Error 404-Page NOT Found', 'attitude' ); ?></h1>
		</header>
		<div class="entry-content clearfix" >
			<p>Thank you</p> 
		</div><!-- .entry-content -->
	</div><!-- #content -->
  <?php 
}

You need to do the same in your child theme. Create a style.css file and functions.php file and unhook the functions.
http://codex.wordpress.org/Child_Themes

If you are unable to unhook then you need to hire a developer to fix it.

Thank you!