how to change pseudo user name

Ivan,
For 4.0+, that's generated in the /components/com_jfbconnect/models/loginregister.php model. Before you modify it there though, I'd recommend looking at the JFBConnect configuration area. In v3.4+ there's an option for "Auto Username Prefix (Facebook User Only):" where you can select from a few predefined usernames.

There really isn't a username from Facebook, other than email though, so not sure you want that. If you do though, you'd have to make modifications to that file, and if you need help, just let us know.

Thanks,
Alex