As you might imagine the Windows Store, since it is the delivery mechanism for Windows 8.1 and app updates, is feeling the brunt of everyone trying to grab the latest bits for Windows 8.1.
It seemed as if Surface RT users were not seeing the update however, it now appears that was also related to the load on the Windows Store as it is delivering the updates.
Thanks to a tip from one of my Twitter followers, @dovellonsky, I was able to force my Windows Store to see the update and allow me to begin the installation.
Just go to this page on your Windows 8 device – http://windows.microsoft.com/en-us/windows-8/update-from-preview# – and you will find two options depending on how you originally installed the Windows 8.1 Preview.
If you get a 403 or Forbidden Error keep trying it will eventually work because I had the same thing happening for about 20 minutes.