upgrade code

Help! I'm a newbie trying to dwonload Congo Jr 5.1 on my 4.3.3 system. I've renamed the exe file, put it in the  software folder on the flash drive. When I boot up and go to settings, my only choice is "please enter your upgrade code here." I cannot find any documentation pertaining to an "upgrade code" in either the pdfs or the on screen help menu. What the hell is it, where can I find it, and will that allow me to download 5.1?

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