GavernWP has an update section which allows to access information whether a theme was updated to the latest version. In order to access an updates panel, you have to use «Updates» submenu from a main menu of theme’s options:
If a theme was not updated, a list of updates will appear; which are newer than your theme version.
However, when you have a theme in the latest version, you will see an appropriate message that a theme does not have any new updates to download.
It’s worth remembering that a free theme — MeetGavernWP is available through a public repository in a github service which allows to easy analysis of changes implemented in particular files. In the case of commercial themes, it is recommended to use tools like WinMerge (Windows) or File Merge (MacOS X) to compare changes in files. Each update in our update system has information about the list of modified files. Generally, it is recommended to compare only these files which you modified manually after loading a theme.