It is probably the configuration of the FPGA chip(s) on the board. These are created by a kind of compiler, usually part of a development system provided (sold, usually expensive) by the FPGA chip manufacturer. To modify it, you will need the original source code or detailed knowledge of the hardware as well as an understanding of the original purpose of the FPGA. You will also need a method to install the firmware onto the FPGA. Often, this is performed with a JTAG interface. There are commercial JTAG dongles available, but they are often part of the FPGA development toolkit as well. The FPGA code is probably considered proprietary property of the board OEM.