See http://arevico.com/remove-duplicate-sub-menu-in-wordpress on how to use this script.

wordpress-duplicate-submenu..php

<?php
/**
 * Remove or change a duplicate submenu in WordPress
 *
 * @author H.F. Kluitenberg
 *
 * See http://arevico.com/remove-duplicate-sub-menu-in-wordpress on how to use this script
 */
add_action('admin_init', 'nameSubMenu') ;

/**
 * Change the submenu name if it exists
 * replace 'arvbb-biblio' with the slug of the parent menu (the one you registered)
 */
function nameSubMenu(){
	global $submenu;
	if ( isset( $submenu['arvbb-biblio'], $submenu['arvbb-biblio'][0], $submenu['arvbb-biblio'][0][0] ) )
			 $submenu['arvbb-biblio'][0][0]  = 'Global Settings';
}