Setting the serial port to the 76800 baud rate for that card can be done the same as any other baud rate. Simply set CWSerial.BaudRate to 76800 before doing a CWSerial.Configure.
However, if a built-in serial port is set to 76800 baud, an error is likely to occur. Use NI-Ports to confirm that certain serial port is an NI-port.