You can upgrade to Enhanced Search 1.1.7 from any previous Enhanced Search release. It will work with any Elasticsearch version we support. This particular version will only become more significant when Elasticsearch 6 becomes their stable release, as there are significant changes to how indexes work in that version. When that happens, if you choose to use Elasticsearch 6, you'll need to be using XFES 1.1.7 or newer. Currently though, there aren't many other changes to account for.