The keyboard has no internet permission, so it cannot look for a new version by itself. Updates come from where you installed it.
- Installed from GitHub: Updates at the bottom of the app shows your version, and Check for updates opens the latest release on GitHub in your browser. If it is newer than yours, download its APK and install it over the old one; your settings and words stay.
- Installed from Google Play: Google Play updates the app like any other, and the button opens its page there.
Every release is signed with the same key, so Android installs a newer APK over the old one without asking anything new.