Second -If you already have Zathras --Best option. Rename your existing Zathras directory then extract the archive in your TBP directroy it will create a new Zathras directory. --Second option. Delete your Zathras\data\cache directory (files now included in the VP), make sure your folders contain no old tables, maps, models, etc, and overwrite your existing directory.
-If you are installing for the first time --Just extract in your TBP directory.
Thrid -Grab the appropriate 3.6.12 inferno builds and updated launcher from the release thread.
Fourth -Run the launcher and select Zathras as the active mod.
That's all there is to it.
*Note if you already have 2.0 beta there are no changes between it and final so no need to redownload.