To change your contact details, go to your "My Account" page by clicking on your name at the top of the page. From the drop down menu that appears click on the "My Account" link.
To Change the Postal Address Where We Send Invoices
On this page, just scroll down to find the address section.
Change your address in the boxes there. Click the "Save Settings" button at the end of the page.
To Change the Email Address Where We Send Invoices
First, click on "Notifications" from the left hand side of the page.
Here, you'll see your email address with two checkboxes to the right of it.
Any address with the "Billing" checkbox marked next to it will receive email invoices.
Either edit your address, or add a new address and mark the "Billing" checkbox, then press "Save Emails."