To upgrade the firmware of the CEC adapter to the latest version, install libCEC 6.0.0 first: libcec-6.0.0.exe
Then click on the Windows icon, type "cec-tray" and start it.
The firmware version is displayed and the upgrade button will be enabled if it can be upgraded to a more recent version.
DO NOT UNPLUG THE ADAPTER WHILE THE UPGRADE IS IN PROGRESS!
Click on the upgrade button and wait for the upgrade to finish:
cec-tray will then reinitialise the connection and display the new version number: