It may be worth reading the pdf in the documentation folder , that will help you understand the BCUSB a bit more .
What type of modem are you trying to flash ?
To load the firmware is easy , connect your BCUSB set your dip switches to the ON position (towards the BCUSB writing on the PCB)
Start the software and press the reset switch in front of the USB connector.
You will then enter DFU mode , load the relevant firmware , Program it and then start the application.
All done