After that, just run the script in your installation path, adding the path of the tarball you want to use to update Pantavisor as an argument:
sudo /opt/pantavisor/update ~/Downloads/x64_appengine_initial_stable.appengine.tar.xz
This will only modify the Pantavisor binary and its dependencies, which are present in the installation path. It will keep the rest of the data intact. For example, it will respect the installed revisions, as well as the Pantacor Hub credentials.