USB-ISS  Multifunction USB Communications Module
Boot Mode Specification

USB-ISS Boot Mode
The USB-ISS  Multifunction USB Communications Module has a built in boot loader. This means the firmware may be updated by the user when a new version becomes available. The boot-loader is based on the USB boot-loader provided by Microchip as part of their "Microchip Application Libraries" and can be downloaded from here.
You may run this program now.

Now place a link on the USB-ISS Boot-loader pins as shown on the right
and connect the USB lead.

The Red LED will light up indicating the USB-ISS is in boot-loader mode.

You should see the following on the boot-loader:

If not, check the 2-pin link on your USB-ISS is in the boot position as indicated above and the USB cable is firmly connected. 

Now Download the required USB-ISS firmware version from the list below:

USB-ISS Firmware Version 2 October 2010 This is the first released version of the firmware (version 1 was internal testing only).
USB-ISS Firmware Version 3 December 2010 Fixed very short Led flash during Comms. It is now a fixed 43mS flash and much more visible.
Fixed random returned bytes in I2C mode when nothing connected. 
It now returns 0xFF's in the buffer as the original USB-I2C module did.
USB-ISS Firmware Version 4 April 2012 Added workaround for PIC18F14K50 errata, Doc-F #2,
which caused SPI crash in commands 0x92 and 0x93 when used with slow SCK frequencies.
USB-ISS Firmware Version 5 April 2013 Added I2C_TEST command to check for the existence of an I2C device.
USB-ISS Firmware Version 6 July 2013 Bugfix. Transmitting one byte in Serial Mode actually sent the full 32 byte buffer. 
USB-ISS Firmware Version 7 September 2015 Bugfix. On power up, I/O's 1&2 are in unknown state (high or low or input). They now power up to input mode
USB-ISS Firmware Version 8 February 2016 Bugfix. If write failed (NACK received) while using the I2C_DIRECT command, bus was held open. 
USB-ISS Firmware Version 9 July 2020 Added support for clock stretching of acknowledge bit within the software I2C implementation

Click on "Open Hex File" and load in the new version, then press "Program/Verify". You should see the following:

That's it!
To run your new version you should remove the boot-loader link from the USB-ISS module and click the "Reset Device" button.
The Green Led will light up indicating normal operation.