Update Release 1 is now available for Revit 2013 products. A few changes have been made this year as to how the updates are accessed. Just a reminder - with the introduction of Autodesk Revit 2013, make sure you are installing the correct update for your product!
For Autodesk Revit Architecture, Autodesk Revit Structure, and Autodesk Revit MEP, you can find the update in the Data & Downloads > Updates section of each product page:
The update for Autodesk Revit 2013 can be found in the Design & Creation Suites Support > Data & Downloads > Updates & Service Packs section.
Installation ReadMe files and Update Enhancement PDFs are available at each of these locations as well.