But then, in going back to the Help page where I originally found the videos, I noticed an "Edit" link for each one, and I found myself able to edit the code for displaying the videos. I changed the size (480 to 960) and hit Save and it saved.
I was confused about why I could edit the web page, thinking something was wrong. After posting this message, I see I was premature in posting a question. I'll shut up now. Sorry for the inconvenience. I just wish I could delete this message.