You can edit a contact's information by clicking on an existing contact. Once you have opened the contact you will be brought to the boaters profile page. There you can view that boaters reservations at your marina, the boats listed on their account, and the credit cards listed on their account.
On the Boats and Credit Card pages, you can also add new boats and cards to the boater profile for future reservations. From this page, you also have to ability to create a new reservation for this boater by selecting "New Reservation" on the top right of the boater profile page.