If you give me info about your purchases, via Discord dms, I can check your purchases and we can send you the updates once that difference is paid.
We are that greedy that we don't mind doing all this manually and waste time to fix the weird system itch.io has (because all of you should be able to just pay the difference).
But you can also reach itch.io and ask for a refund or tell them you only want to pay the difference.
We understand nobody likes paying more for something that previously had a smaller price. But the game now has a final product price and the previous price was only for the update, just like in Patreon.