Q:
Crafting Agony Resistance Infusion
The method of upgrading AR infusions is stated to be by using Artificer, which likely means at a crafting station using raw items. Additionally, the current implementation of upgrades is that you can’t freely remove them from items to do this. I agree that this is a bad way for things to be – ideally you’d be able to drop a +6 infusion an an item that already has a +6 infusion, spend one reagent and the item’s infuson would upgrade to +7 as if upgraded via the artificer recipe.
There are claims of a datamined Upgrade Extractor, and above a certain threshold of infusion upgrades, it would be cheaper to use that than to craft a new one. Below that threshold, the assumption can be made you’d just have to destroy the old infusion because it’d be cheaper to craft a new one.