Windows BT is a hidden folder at the root of the drive that contains the esd. Make sure you have hidden files and folders view enabled in explorer settings
It moves the file when it decrypts it. It's in something like C:\$BT~Windows or some such nonsense as install.esd after decryption.
when you upgrade and finish the upgrade installation the file from C:\Windows\SoftwareDistribution\Download auto deleted....
If your currently downloading I don't believe you'll see it. You have to first finish download to get it