Well, it turns out that we fixed a bunch of issues as well as adding Gantry 2.0. When we added 2.0 it will 'work' with just updating the Gantry lib folder, but you won't get any new functionality. This is a pretty major upgrade, as you can see from the release info where we outline all the changed and new files:
The best thing would be to see if you have modified any of the 'changed files' listed. if not just copy the new ones on top of your existing ones. If you have then you will need to diff the new files to make sure your changes are retained.