I know I sure had a lot of trouble upgrading! I did all the updates like I was supposed to and the download would just not show up in the store! Very frustrating experience. So I did was all good IT folks to - Googled it!
The end procedure was simple actually:
Crack open IE on your target upgrade box
Paste the following link in your address bar and hit enter
ms-windows-store:WindowsUpgrade?ocid=GA8-1_O_WOL_Hero_Buy_81Update_Null_01
This should open the Windows Store to a nice Windows 8.1 download
Click download and wait for it to start prompting you for action
This procedure seems to work for both Windows RT and Windows Pro. Special thank you to francescob who was kind enough to post the above Windows Store link in the comments section of this article.