A short, practical answer — written the same way the product talks to you: plain language, one decision at a time.
This article is part of the credits & billing set. The behaviour it describes follows the same three rules as everything else here: the price is shown before the action, nothing we infer is locked, and no work you have already used is rewritten without telling you.
Open the relevant screen and make the change. Editing is always free — only generation costs credits, and the cost is on the button before you press it.