As we all know in this thread, logging in as the Administrator user with the administrator permission still did not get the ability to successfully download Win8.1 from the Store.
I ultimately called Dell Care who looked at the Service code of this Dell laptop, recognized the machine was registered to Costco (where I purchased from) and saw Costco as the 'ultimate' administrator. Dell Care changed the ownership from Costco to my
Microsoft account. Logging out as Administrator and logging in as my Microsoft user account which NOW had ultimate 'administrator' privileges allowed the 8.1 download to start successfully without the familiar message "You
need to use an account with Administrator privileges to install Windows 8.1 try logging in with the user account of an administrator of this PC and trying the upgrade again."
Bottom line: the local Administrator account does not have the 'ultimate' administrative privileges. Your Microsoft id account needs this - and you have to figure out how to connect that 'ultimate' access to your Microsoft user id. What a PITA.
If you have a Dell laptop, make the call to Dell Care to avoid serious frustration.
Good luck to those without Dell Care. Perhaps the place of purchase can assign the necessary permissions to your Microsoft user id which was the ultimate solution to this issue.