We release new versions of the Unity plugin at regular intervals. Each new version introduces improvements our back-end software and in order to get the benefits, you need to upgrade the plugin in the Unity project.
At best it's as straight-forward as re-importing the Unity plugin, the same you do when installing it.
If this doesn't work, or you get errors, you need to delete all Umbra-files from the Unity project and then install the new version from scratch. Deleting Umbra from a project is as simple as deleting any Umbra-named folders inside the project.
After this, import the plugin as per normal.