To upgrade, you simply need to download the latest version from the "My Subscriptions" area, and install it like a new extension. There are a lot of new settings and features since v3.2, which it sounds like you were using, but everything should continue working how it was.
You can see the version you're using in the JFBConnect Overview page in the admin area. Look for "Installed Version".
For full documentation on upgrading or about the new configuration settings in JFBConnect v4.0, see:
Upgrade Guide:
www.sourcecoast.com/jfbconnect/docs/upgrade-guide
Configuration Guide:
www.sourcecoast.com/jfbconnect/docs/configuration-guide