Update

You can update or revert the underlying version of Arctic Viewer from the about page. Tapping on the input bar will bring up a picker wheel where you can select the version you want to use. When the download button is pressed there is no way to cancel, it's a small package and will download and and overwrite old files very quickly. You can always re-download a newer or older version. You can also download the master branch of Arctic Viewer which is the latest possible version. Note, however, that there is a possibility it's unstable.

Arctic Viewer neither automatically downloads new versions, nor automatically fetches a list of available versions. Periodically press the refresh button to get a new list of versions.