I want to update my user meta table

changing the code as below gave me my answer :

$userdata = array(
    'user_login'  => $_POST['usname'],
    'user_pass'   => $_POST['passw'] // When creating an user, `user_pass` is expected.
);

$user_id = wp_insert_user( $userdata ) ;

update_user_meta( $user_id, 'address', $_REQUEST['address'] );
update_user_meta( $user_id, 'age', $_REQUEST['age']);
update_user_meta( $user_id, 'class', $_REQUEST['class']);

//On success
if ( ! is_wp_error( $user_id ) ) {
    echo "User created : ". $user_id;
}