As the "SuperOwner" of a room you have the option to Ban & Un-Ban guests from your room. There are a couple of options that you can use to achieve this.
First you can use the room commands. To see a list of supported room commands you can type /? into the room or right click in the chat window and choose "commands" from the popup window.
The result will look like the following:
Commandline commands supported in this client: FixScroll, Reconnect, Disconnect, Hop, Sizzle, Clear, Away [<Away Message>], Unaway, Nick <Nickname>, DebugPrint, ShowGuestpassStored, SaveGuestpass <Guest Password>, Kick <kick message>, Ban15m <ban message>, Ban1h <ban message>, Ban24h <ban message>, Guestban, Guestunban, Guestmircban, Guestmircunban, INVITE <username>, TOPIC <topic message>, WELCOME <welcome message>, +/-PROTECTIONMODE. Commands must start with /
In this list of commands you will see Guestban, Guestunban, Guestmircban, Guestmircunban.
/Guestban will ban all guests from entering your room.
/Guestunban will remove the ban of all guests.
/Guestmircban will only ban guests using 3rd party clients to connect to chat as a guest.
/Guestmircban will only remove the ban of 3rd party clients chatting as guests.
This does not kick the current guest nicknames in the room. It only prevents them from joining.
The other option is to use the SuperOwner Room Access dialog which you can access using the room popup menu.
To add a guest ban you click the Add Access Button. Then in the entry box add >*
Choose the Deny time limit and press the Add Access Entry button. You will see the entry has been added. You can remove the ban by removing the entry.