The legally-required address at the bottom of email footers is derived from your account's address info. If you need to change it to another address of your organization, you can easily do so from within the email editor. You can also change the physical address on the scheduling page, or in your account's settings.

If you're referring to the email address shown in the "this email was sent by" bit, that is derived from the From: address in the header, which can be changed in the email editor or scheduling screen as well.