Go to your account overview. Under your blue tabs at the top you will see several headings; all the way to the left is "profile". Hover over it and it will offer a drop down. Just choose "add or change address", change it and you're done.
i just bought something, and didn't change the mailing address to my new address. how can i do that?
You can't change the mailing address on an already sent payment. You need to contact the seller. The seller may want to refund the payment and ask you to resend it with the correct mailing address.
