Ok, can you tell me exactly where I would need to make this change then please?

<?php

/**
* displays add to wishlist sidebox
*
* @author untitled
* @version 0.1
* @since 0.1
* @access public
* @copyright untitled
*
*/


$content = '';
if ( $_SESSION['customer_id'] ) {

$content .= zen_draw_form('un_wishlist_sidebox', zen_href_link(UN_FILENAME_WISHLIST, '', 'NONSSL'), 'get');
$content .= zen_draw_hidden_field('main_page', UN_FILENAME_WISHLIST);
$content .= zen_hide_session_id();
$content .= zen_draw_hidden_field('action','un_add_wishlist');
$content .= zen_draw_hidden_field('products_id', (int)$_GET['products_id']);
$content .= '<div align="center">';
//$content .= zen_image_submit(UN_BUTTON_IMAGE_WISHLIST_ADD, UN_BUTTON_WISHLIST_ADD_ALT);
$content .= '<input type="submit" value="' . UN_BUTTON_WISHLIST_ADD_ALT . '" />';
$content .= '<br />';
$content .= UN_BOX_WISHLIST_ADD_TEXT;
$content .= '</div>';
$content .= '</form>';

} else {

$content .= '<div>';
$content .= UN_BOX_WISHLIST_LOGIN_TEXT;
$content .= '</div>';

}


?>