Sending the code via RS232 serial port is only necessary for those that don't have a remote control. If you have a Bryston remote control you just press the Code button followed by 245 and whatever input is currently selected will be programmed as a unity gain "bypass" input.
If you don't have a remote control then you will need a computer with a serial port (or a USB > Serial Port adapter), a fairly standard serial "null modem" cable available at most computer and electronic shops, and a terminal program to send the 245 code from (Windows XP has the Hyperterminal program, but it was removed from Windows Vista on).
Do you have a remote control?
Steve