JFBConnect was architected to upgrade from one version to another without issues. You shouldn't run into any major hiccups when you upgrade to 8.0. However, many settings and options will have changed. The settings that can be upgraded will be done so automatically, but you'll need to definitely want to go through all the settings in JFBConnect to make sure things are setup how you want.
With any upgrade though, even between minor updates, we recommend testing an upgrade on a development or backup site first. With such a large jump, that's even more highly recommended.. or at least have a full backup of your site before you make the upgrade so that you can rollback if necessary.
Thanks,
Alex