Currently it's very easy to accidentally upgrade/downgrade someone between pro/ultimate on the members page.
What I'm proposing is a system where the first time the user clicks on an a button in the 'plan' column to change the plan of a member, it gives a popup to ask if you're sure you want to change their plan.
IF the user acknowledges that's indeed what they want to do, then any further changes to plans while they're still on the page should be able to happen without further confirmation dialogs. This should be remembered for as long as the page is loaded. If they refresh or return to this page later, it should once again ask for confirmation
