If the address field is greyed out it means the patron’s address belongs to another patron, so you need to edit the address in the address owner’s account. Click the blue coloured link of the address owner’s name. The address owner’s account will be opened in a new tab. You may edit the address there, which updates both records.
If the address is no longer shared and patron needs a new address on their account, click New Address in their account , enter the new information, select both Mailing and Billing buttons, and save the record. The old address will be overridden with new, and the address field is not greyed out.
For more information on managing patron accounts, see http://docs.libraries.coop/sitka/_update_patron_account.html#_unlinking_shared_patron_addresses