Adding this code at bottom worked.
function modify_jquery() {
if (!is_admin()) {
wp_deregister_script(‘jquery’);
wp_register_script(‘jquery’, ‘https://code.jquery.com/jquery-1.11.3.min.js’);
wp_enqueue_script(‘jquery’);
}
}
add_action(‘init’, ‘modify_jquery’);

Thanks Amigo

Question 2. What is the optimal image size for the full screen slider?