As we showed in the previous tutorial, the device must be changed to bootloader mode before we can perform a field upgrade.

That is, you the developer must decide on some special thing that the user must do, like pressing a secret button or sending some special values to the device, to get your target firmware to jump to the bootloader code in the device.

Once the user has done that, and has connected his device to the PC via the USB, he can run the BLPro.exe program.  As we said in an earlier tutorial, this program should be in the same directory as files BL.ini, logo.bmp (or logo.jpg or logo.gif), AND the hex file that contains the new firmware upgrade. 

(In our case, that firmware upgrade file was called AryTst5_2550.hex.)