OK it would appear the updates are a part of the Subscription Advantage pack I blogged about below however you can get hold of the Update 2 for your flavour of Revit from the Updates section of each product page:
Autodesk Revit Architecture 2013 UR2
Autodesk Revit Structure 2013 UR2
Autodesk Revit MEP 2013 UR2
The update for Autodesk Revit 2013 can be found in the Design & Creation Suites Support > Data & Downloads > Updates & Service Packs section.
Autodesk Revit 2013 UR2
Installation ReadMe files and Update Enhancement PDFs are available at each of these locations as well.