How do I ban the ip of someone of my server?? its not rented from lfs.net
and the guy keep creating accounts and joining in, its really annoying.

You can't IP ban in LFS.

Your option to prevent them from joining is to firewall their IP (if possible).

Airio (I think) has the ability to track people by IP. You could maybe create an IP ban list that way (but I'm not certain).