Update Default Jquery of WP

function modify_jquery() {
     if (!is_admin()) {
            wp_deregister_script('jquery');
            wp_register_script('jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.8.1/jquery.min.js', false, '1.8.1');
            wp_enqueue_script('jquery');
     }
}
add_action('init', 'modify_jquery');