For one part of one page wouldn't it be worth it to spend an hour with someone there at 'the computer station' and teach them how to use a simple FTP client? It's not a pretty solution but you could just keep a backup of their site and save a template of the HTML file on their desktop with a short printed guide taped to the desk.
I've had to do similar things with clients/friends in the past and, if you do it right, at most will get a follow up phone call the first time they do it on their own.
"...the adversities born of well-placed thoughts should be considered mercies rather than misfortunes." Don Quixote