For this upgrade loader step you have to use serial cable. Below are the steps:

1. Connect the the unit with the serial cable and connect the LAN port from PC to the board. (Please make sure the PC and the board are in the same subnet)
2. Run Tera Term on the PC/Desktop.
3. Power up the unit, at this time when you see in Tera term status is loading firmware at this time you press ESC button (At keyboard) for few times.
4. In Tera term, it will show you list from 1 - 7
5. Press 5. "Update Flash....".
6. Press 1. "Update BIOS..".
7. After that use normal TFTP to put in the file to board.