Downside - I did as you said, but even though I changed to All Files, it is still a text file, and when I click to open, I don't get an option to Run.
I checked the link you gave and it does say For Windows 8.1 Update I should have installed KB3035583 and KB2976978. I've checked on recent updates and I have both of these, KB3035583 installed 20.5.15 and KB2976978 installed on 6.6.15. So perhaps my laptop is ready for Windows 10 without my having to do anything.
Lizzie