Hmm, don't exactly remember... open the console and type:
\rconPassword <rcon_password_you_set_in_server.cfg>
\rcon kick <playername>
Though I very much suggest that you use TJW's or R1CH's Code. For example with TJW's Trembot you can:
!kick <part_of_player_name>
or
!listplayers
!kick <slot_of_player_shown_in_!listplayers>
(for those guys with unread/writeable names)