For some reason unknown to me, XTU v4.2 has not yet been published on the public Intel download site. You can already get the update by enabling automatic updating in the settings menu of XTU. For those who want to use the standalone installer, I have temporarily uploaded the file to our server. Note that the file will be removed once it is up on the Intel download site.
For more information on the changelog, check out this article: "Extreme Tuning Utility v4.2 Released - Introducing AppTune, Support for Sandy Bridge(-E), and WinBlue Update