Login with facebook results in white page

You can use the Update button from the Overview area of JFBConnect to update the main component. The Joomla Update Manager should be able to update the Kunena profile plugin, but there's sometimes issues with that.

If you need to download the full package, you can just install it as if it were the first time. You don't need to uninstall first and you won't loose any settings in the process.

Hope that helps,
Alex