I know I can update from 1.1.0 to 1.1.3 and tried to do that. I uploaded the upgrade files three times and every time, I get the same message: "You are already running the current version (1.1.0). To do a fresh install, click here."
So I went on the upgrade help page: http://xenforo.com/help/upgrades/
It said: "If the upgrade system says that you are already running the most recent version, repeat the Uploading step, as the files were not overwritten correctly. Ensure that you are in the correct place and that correct files are being overwritten."
Obviously, I re-uploaded three times using not only 1.1.3, but 1.1.2, and 1.1.1.