Windows 8.1 upgrade download location [duplicate]
The ESD file should be stored in C:\Windows\SoftwareDistribution\Download
You should also take a look into the WindowsUpdate.log it should show the link to the file.
After download and before continuing installation I found the install data in C:\$Windows.~BT\. I am willing to create an ISO file from this installation data.
But I think you can create a recovery media by following this article after upgrading: Create a USB recovery drive