If you followed the instructions in the Setting Up Credit Card Processing article, you will be automatically set up to accept Visa and MasterCard.
DaySmart Payments Customers
Discover: DaySmart Payments customers are automatically setup to accept Discover cards when they sign up for processing.
American Express: When first signing up for DaySmart Payments, you will be asked if you wish to accept American Express. If you declined that option previously but wish to add it now, you will want to give DaySmart Payments a call at 800-982-6419.