stupid question how do you get these stainless wiper arms off?

That kit was the one I described and linked here. It appears to have been discontinued. I still find some listings online (such as this and this), though it'd be a cross-your-fingers-and-confirm-stock-first deal, because currently popular practice in online sales is to list every part ever made as though you can buy it, but then when you go to buy it, "Oh, sorry, that's out of stock. But here, let us interest you in [completely irrelevant part] instead!".