Upload the FW
To upload you need a FTDI cable like this: Link (Also make sure that you have the FTDI driver installed) (Unfortunately 3DR obv. stopped selling those cables so the link above is dead)
After you connect it, open Config. Tool, and select the right port.
Open Confg. Tool, than click on "Options" menu than Update firmware.
Browse for the firmware file (.hex) The firmware file is located at your Config_Tool_directory\FW & Char\
MinimOSD will show the version of your firmware on boot