Revit Update 4 (or Revit R2) is now available for subscription customers:
To download, go to your subscription site and check the listings for new product enhancements. Click the link for the appropriate Revit download and follow your nose from there.
Note that you should have Revit Update 3 installed before installing Update 4 (R2).
In particular, I'm excited about the prospects for much more viable site creation/editing tools in the Site Designer - which you can download and install from the App Store - again for subscription customers only.