OK. This is a little complicated, and I'm not sure how well I can explain it, but:
The main zip file is not password protected. It would have started to extract by itself, which is an issue we will have to address in a minute. However, inside the main zip, there is a second zip, and that's the one with the password. Good news, you don't have to mess with it. I'm assuming your SD card now has a couple extra files and folders. You may have to start all over, but let's try this first:
1,) go to pad - file manager - external disk.
2.) erase everything on the SD card except the main zip file.
3.) rename the main zip file from *.zip to *.yuneec
4.) back out of file manager
5.) restart the ST16.
6.) start the update.
If that does not work, you may have to format the SD card and start all over. As noted above, some PC systems can't read the file extensions correctly, so you can't change it. And some browsers change it for you. The file manager in your ST16 will always work.
By the way, the video above is good. The problem is he had downloaded the file with a system that corrected the file name for him, and he apparently never noticed.