August 24, 2015 - JFBConnect v6.4.2 is available now. Facebook breaking changes.
See the full changelog.
You don't need to. You just need to install the main com_jlinked...zip file as if you were installing for the first time.
Doesn't hurt to uninstall first. Either way, all of your settings will be retained. It should be a pretty smooth upgrade process, but if you run into any issues, just let us know.