First you need permission to make changes in db of www.wordpress.domain.com. So for this you have to add the ip of wwww.wordpress.domain.com to www.doamin.com so that they allow to make changes. After that just make a function which allow you to connect to that server and make changes. The query for this is
$pwd = $_POST['pwd'];
$email = $_POST['email'];
$website = $_POST['website'];
$description = $_POST['description'];
wp_update_user( array ('ID' => $userID, 'user_pass' => $pwd, 'user_email' => $email, 'user_url' => $website, 'description' => $description) ) ;
The function wp_update_user is in resgistration.php. But you can make changes by making own query. You can see the field names here. so make changes as you wish.