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 enterms-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