That would probably be under, uh, billing, manage account.
It depends whether you have automatic billing set. You can always make a payment using the, uh, make payment link.
Usually the notification emails are thorough. Didn't they say what to do?
[color=#00CC00]ANONYMOUS0 => Max Discount[/color], [color=#6600CC]ANONYMOUS2 => Max Discount less $1[/color] or Cut the code, [color=#CC0000]it's their birthday:[/color] [color=#00CC00]9999 => $99.99 Off[/color]