It use to be something like this:
Connect to your SEPM server.
Browse to the following directory: c:\program files\symantec\symantec endpoint protection Manager\Inetpub\Content
Open the contentinfo.txt file and locate the version of SEP you are planning on updating the defs on (32 or 64 bit)
Open the directory corresponding to your version
Copy a zip file (full.zip) from the latest revision, to your installation file directory
Delete the vdefhub.zip file
Rename the other file to vdefhub.zip