Of course you can. This is actually a good idea to keep your account active.
Any payments will be added to your "available funds". And when your payment is due, the amount will be taken from there.
Yes you can. Note that this is a prepaid service, there are no refunds or prorating of plans.
Once you log into your account, look for Account Status.
That's all. The change is locked in at that price and will occur on your next renewal date, as long as autopay is setup.
You don't need AutoPay to change plan.
AutoPay is adding your credit card to your account to sign-up for preauthorized payments.
Also when you sign up for AutoPay, you automatically get $2 off your bill every month.
you can put funds or what PM calls CREDIT at anytime and if you want to get ahead of the monthly cycle you can load the upcoming month's payment onto the balance so the remainder of the month at hand which is paid for elapse an then on the day when your monthly cycle rolls over the funds from the positive balance simply drop into the account and if all goes well it should automatically renew your monthly plan.