@robsmit You follow the instructions in the Release notes (http://xibo.org.uk/manual/en/release_notes.html) which you should be reading as part of your upgrade proceedure - so you know what has changed and any implications for your installation). TLDR, you just replace settings.php from your old installation and it will then know to do an upgrade. There are some caveats.
We support upgrading to 1.7.7 from any version of Xibo. It’s too complex to figure out which files need to be removed each time. It’s trivial to remove the old CMS files at upgrade, so that’s the way we do it.
If you need a single button press upgrade then Spring Signage (and possibly others too) offer that as part of their Cloud hosting offering.