brianmjc, start over and follow the instructions exactly as I provided please. As Steve mentioned, you did an INSTALL, which is the wrong way to update. The local install is not needed. If you make a backup (step 1), you can do this on your live site. If something goes wrong, you can revert to that backup and we can assist further.
If you have any questions about the rules/customs of this website, feel free to send me a PM. My little corner of the world, where I sometimes post things documented from my job.
Thanks. So I abandoned the other route and followed your instructions. I got a general 500 Internal Server Error page when I tried step #8.
There are a few things that I can think of offhand which may have resulted in a problem. First, I was unable to do step #2 since I cannot access the forum's ACP. I tried searching for a way to do it via phpMyAdmin, but to no avail. I do have an active style that's not Prosilver, so I opted to search for anything related to styles in the database. I found and edited the phpbb_styles table, setting the Active status of all styles except Prosilver to 0 (three additional styles were installed, and they were all set to 1 before). But this made no difference on the live site; the alternate style I had active was still active. So I left it and proceeded, keeping my fingers crossed.
I was also unable to perform step #4. Again, because I cannot access the ACP. I recall that reCaptcha was definitely a functional part of the forum (i.e. registering a new user required it), but I don't recall installing a plugin to add it. I do not think I added any plugins, in fact.
Finally, I opted to skip files that already existed on the server while uploading the fresh phpBB files, such as images/index.html. Was this the correct move? They seemed identical when I brought some of them up in Notepad++.
I did download both my database and all files as they were to my local computer as a precaution.