We would be happy to help you make this change in your account! Is this website address a link in your email, or the address listed in your Organization Information? If you are looking to update a link in your email this can be done by clicking into the link that is currently there, selecting Link in the editing block, then choosing Edit in the drop down.
On the other hand, the website in your Organization Information can be updated in the My Settings page of your account.
I hope these answers help!