Autodesk has released Web Update 1 for Revit® Architecture 2013. Both 32-bit and 64-bit versions are available, with separate downloads for each version. The update is available to users who have purchased a valid license for Autodesk Revit Architecture 2013 or a product suite including Revit Architecture.
The update is not a full installation, but instead is considered a service pack so the 2013 version must already be installed.