Thanks for getting back with me so promptly, Natasha, but new subscription plans are not available to me on a simple point-and-click basis now that I'm at the 2999 MB level. All of the upgrade options are "grayed out," in that they are marked with an asterisk as "n/a."
The only info I see is, "To UPGRADE, use the same PayPal account." But there's no way to do that! If I go to PayPal, I don't see an option to increase my subscription.
The last time I needed an additional GB of storage, I had to write in a special request to email@example.com and then wait for several days!
Your upgrade system needs revamping, sorry to say. No, it is not automatic for your larger accounts; it's as though customer service dries up as soon as we start paying more!