Use pre_get_posts to change the ordering of category posts to the title.

wordpress-change-category-order.php

<?php

add_action( 'pre_get_posts', 'prefix_change_category_order' );
/**
 * Customize category Query using pre_get_posts.
 * 
 * @author     FAT Media <http://youneedfat.com>
 * @copyright  Copyright (c) 2013, FAT Media, LLC
 * @license    GPL-2.0+
 * @todo       Change prefix to theme or plugin prefix.
 *
 */
function prefix_change_category_order( $query ) {
  
	if ( $query->is_main_query() && ! $query->is_feed() && ! is_admin() && is_category() ) {
		$query->set( 'orderby', 'title' );
		$query->set( 'order', 'DESC' );
	}

}