When you change your account type, you will see your expiration date change immediately. Your account takes the remaining time period left on your original expiration date, and adjusts it based on the cost of the new account type you have shifted to. You'll see the change on the web right away.
Because people frequently make a series of changes to their accounts in a single day, the billing system doesn't send you an email until the end of the day. (Just in case someone is making unauthorized changes to your account, we do send notices of account changes as soon as, and every time, they happen.) At the end of the day, you will receive one of two emails:
Under our new billing system, there is one significant change to upgrades. Under the old system, you would have 2 weeks to pay your bill, and, if you did not pay your pro-rated bill, you would automatically be downgraded to your old account type. Under the new billing system, you will never be downgraded unless you request the downgrade; it is not required to pay your pro-rated bill. Your account's expiration date will simply move forward, and you will receive your next annual bill (at your new account type's rate) sooner.
If you have pre-paid for multiple years, and wish to try a new account type without having to pre-pay at the new rate for multiple years, we recommend that you simply ignore the pro-rated invoice. If, at some point in the future, you would like to pay to extend back to your old expiration date, just let us know, and we'll send you one.