Hi Peggy, I expect you meant the main XML sitemap, not the images XML sitemap.
You can edit the array of items that get outputted to the sitemap in /modules/XML_Sitemap/config.php
Code:
3 => array(
'type' => 'S',
'items_function' => 'xmlmap_get_pages',
'properties' => array(
'lastmod' => '',
'changefreq' => 'never',
'priority' => '0.2',
),
),