Go to Checkout >> Online Payment Manager. Then select your payment gateway, and click edit. Fill in the same information that you would use to login to merchant account's site. When that is filled out, click Save Changes to Selected Gateway, and you are all set! You may begin accepting payments for orders placed.
Note: You will be redirected to the Payment Gateway Selector/Editor- from here you will need to select your gateway from the dropdown menu and click Enable Gateway.
