Hello snowbird,
If you refer to the address for shipping labels, you can modify this after logging in to your account by selecting 'Shipping Labels' from the My Account menu. If you refer to the address related to shipping insurance, you can update this by selecting 'Auctiva Shipping Ins.' from the My Account menu after logging in.
However, if you are encountering this in another location, such as a custom email (which can be modified by selecting 'Manage' in the email section of the eBay Sales menu) or elsewhere, please let us know in a support case exactly where you are encountering this so we can assist you further.
- Craig