1. Go to the contact's constituent record.
  2. Go to the Relationships tab.
  3. Edit the relationship with the organization.
  4. Go to the Contact Information tab.
  5. Edit or Remove the contact address to the correct address to mail to this contact.  If you remove the address, it will mail to the contact at the organization address.  If you leave an address here, it will always mail to this address when mailing to this organization's contact.