There are four ways to upgrade/recover the firmware of Galileo:
- Through the Arduino IDE.
- Through the Force Recovery Mode.
- Through the UEFI internal shell.
- Using a Dediprog.
Using the Arduino IDE is the easiest way, however, if your board is not recognized by your PC you won't be able to perform this method.
Using the second or third way: Force Recovery Mode and UEFI internal shell, you will need access the Linux Terminal and the booting process too, so you will need the Serial cable for that.
The other option would be to use a Dediprog that doesn't required the Serial cable. However, I think it would be easier to get a Serial cable than a Dediprog.
For the Force Recovery method there is a guide here if you want to check it: Intel® Galileo Board Recovery Mode.
For the UEFI internal shell method there is an explanation about it in the following document, in section 10: Intel® Quark™ BSP Build and Software User Guide.
The method using a Dediprog is explained also in the same document, in section 11: Intel® Quark™ BSP Build and Software User Guide