March 23, 2015 - JFBConnect v6.3 is available now. Joomla 3.4 compatibility updates, Yahoo authentication, front-end social network connection management and more.
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.