Hello Dave,
I am really sorry for the confusions. Upgrading from EasyBlog 3.8.x or older to 3.9.x requires a full uninstall / installation. The reason is because there are some core files which were modified in this release and running the updater would actually break things.
Rest assured that your data would not get erased when you perform an uninstall. Theme files and other core files would however get erased, so if you have made any modifications, it's best to make a backup of the modifications first.