Wordpress Display Name Change

/**
 * Change Default Display Name (Powered by yeahhub.com)
 */

function change_display_name( $user_id ) {
 $info = get_userdata( $user_id );
 $args = array(
 'ID' => $user_id,
 'display_name' => $info->first_name . ' ' . $info->last_name
 );
 wp_update_user( $args );
}
add_action('user_register','change_display_name');