Need help setting Firmata baud speed

I'm trying to set firmata to use a baud speed of 9600, but can't seem to work out how? I've tried changing Serial.begin(115200); to Serial.begin(9600); in firmata.cpp but I can't seem to save the changes I make to the file? I've tried deleting firmata.o before I make the change but that doesn't seem to make any difference.

Am I on the right track at all?

Thanks for any help.