Hello Simon,
All of these settings are found in the NioNode block, on the SerialRATC tab. You set whatever values you which, matching the baud rate (though there are settings higher, do not exceed 56k). Using the web interface, you will want to check the status of the 232 port. Here are the instructions on how this is done;
http://peaveyoxford.com/kc/index.htm#5310
BTW, You may find this helpful as you move forward;
http://peaveyoxford.com/kc/index.htm#2051
Read the introduction, and then move to the specifics of RATC2
Good luck,
Fergy