YOU CAN NOT UPGRADE ON A BROWSER. THESE DIRECTIONS ARE FOR THE APP
1) Go to the Microsoft Store / Movies & TV app on a PC(Go to the search bar on your PC that says "Type here to search" and type in Movies & TV, find the app)
https://www.microsoft.com/en-us/p/movies-tv/9wzdncrfj3p2Â
5) Microsoft will ask you to sign in and confirm your purchase
(Xbox no longer works to upgrade)