In index.php replace:
$additional_loop = new WP_Query("cat=".$k_option['mainpage']['feature_cats_final']."&posts_per_page=".$k_option['mainpage']['feature_count']);
$additional_loop = new WP_Query(array('post_type' => 'page', 'posts_per_page' => 5, 'post__in' => array(37,50,54,30,32)));
Instead of 37,50,etc. insert the ids of the pages you want to display. Set the posts_per_page parameter to the number of pages you want to show (i.e. 5).
Where can I find the page id?
Log in and go to the page which you want to add to the slider. Click on "Edit Page" in the top wordpress admin bar. You'll see that the url of the page editor contains a number (like http://localhost/wp-admin/post.php?post=50&action=edit ) - i.e. this page has the id 50. Note the ids and insert them like instructed above.