1) You can check your project properties or the .mymetadata file for the j2ee-spec version. Servlet 2.3 spec was J2EE 1.3, Servlet 2.4 spec was J2EE 1.4, and so on.
2) If you mean the j2ee spec, you can change the value in the file I mentioned above, save, and close/reopen your project. You may also want to change the J2EE Library Set that is in your build path. We ship 1.3 and 1.4 library sets.
3) We offer no upgrade path between versions because the list of potential breaks for more complex projects is unknown. So instead users need to do this manually. Besides updating the libraries, you can update your .mystrutsdata file to increment the version to I believe version “2” is recognized as 1.2.