Hello everyone,
Hopefully the following is helpful. It took me many, many searches to find this, but here it is. I haven't tried it yet with my 4+ year old Star Adventurer, so I cannot make a claim that it's the "correct" software.
The Motor Controller Firmware Loader (version 1.64) for the original Star Adventurer can be downloaded from https://www.opticalvision.de/service/downloads/
This site seems to have lots of useful SW software. Just keep scrolling down until you see "STAR ADVENTURER MOTOR CONTROLLER FIRMWARE LOADER V1.64" - look for this:
I downloaded the file, unzipped it, scanned it - no viruses, spyware, or any other threats were found.
Good luck!
UPDATE --- April 20, 2020 --- AS FAR AS I CAN TELL, THESE ARE THE LATEST APPLICATION & FIRMWARE VERSIONS, EVEN THOUGH THEY'RE A COUPLE OF YEARS OLD --- I downloaded the "latest" MC Firmware version 3.6.07 from SkyWatcher's site, ran the Motor Controller Firmware Loader version 1.64, and was able to successfully install the firmware update to my Star Adventurer. Went very smoothly, and without a hitch!