It's important to point out here that this was my experience only and others may have found the upgrade process a walk in the park. Anyway, I'd been mulling it over for a while and decided to take the plunge on Saturday last, having backed up everything in preparation. It's also worth pointing out that the upgrade is $44.99 if you're upgrading and in my case, I was able to upgrade Gallery at no cost because I'd bought it after Jan 4 2018. This link explains the pricing. Following their guide here, I put the forum into maintenance mode, updated all modules that could be updated by adding package servers. Some are dummy updates only, in preparation for updating when the core has been updated. At first sight the guide looks a little scary if you're not used to this kind of stuff, but if followed sequentially, it all makes sense. During the update process, numerous conflict messages appeared and the only way to proceed was to uninstall non-compatible plugins, but that wasn't a problem since they could be reinstalled later. In my case, the upgrade hung half way through and I had to abort, leaving the site in an unusable state. Eventually, and after a few days, a fellow WoltLab customer whizz kid and one of the devs at WoltLab helped get the site back up (from a backup) and we were able to finally upgrade, having put a privacy password temporarily on the root to stop any interference. The experience was very frustrating and in fact the dev encountered the very same problem that I had, but was able to fix it since he had more tools and experience at his disposal. If I were to carry out this upgrade again, I would remove practically every plugin first and definitely slap a password on the root directory. The forum now works perfectly and I'm very glad I upgraded, not to mention having learned a few things along the way. Kudos to Alexander at WoltLab for his expertise.