[Solved] display name

@ngocvy,

You should change the value of the "Display name publicly as" option. Navigate to Dashboard > Users admin page edit the user profile and change the value of the option. 

The plugin just updates the first and last names, but not the value of the "Display name publicly as" option. 

add this code to function for who stuck like me

add_filter("wpdiscuz_comment_author", 'custom_comment_author', 10, 2 );
function custom_comment_author( $authorName, $commentID ) {

$comment = get_comment( $commentID );
$user = get_user_by( 'email', $comment->comment_author_email );

if( !$user ):

return $authorName;

else:

$firstname = get_user_meta( $user->ID, 'first_name', true );
$lastname = get_user_meta( $user->ID, 'last_name', true );

if( empty( $firstname ) OR empty( $lastname ) ):

return $authorName;

else:

return $firstname . ' ' . $lastname;

endif;

endif;

}