This is my third attempt at an upgrade from 1.3.2 -> 2.5. I have given up on such a large jump and I am now moving from major release to major release (i.e 1.3.2 ->1.4.2, then to 1.5.x, and so on).
Currently I am on release 1.4.2, but I can’t seem to change the theme. There was a custom theme in 1.3.2 but it causes a fatal error in 1.4.2, so I am trying to switch themes.
When I go to Settings -> themes the current Theme is blank. All is see is Current Theme: “” , I was hoping to Current Theme: “Rhythm”.
Each plugin should be upgraded at the same speed than the core (use the version of plugins that is released just after a major release of Omeka).
Anyway, set the default theme and try to upgrade only the metadata. When you will be in Omeka 2.5, you’ll install the official updated theme and re-apply your customization on it.
If you want to upgrade to Omeka S too, I just wrote a plugin that installs it and upgrades metadata, files, params and theme directly from Omeka 2.3.1+ (https://github.com/Daniel-KM/UpgradeToOmekaS).