WordPress load its own copy of jQuery into your theme. But there are some advantages loading jQuery from google CDN.
Paste the code given below into your functions.php:
function load_googlecdn_jquery() {
if (!is_admin()) {
wp_deregister_script('jquery');
wp_register_script('jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js', false, '1.8.3');
wp_enqueue_script('jquery');
}
}
add_action('wp_enqueue_scripts', 'load_googlecdn_jquery');