The Paradigm deck is the list of paradigms available to your party in battle. To modify it, press to open the main menu and then select Paradigms. Via the menu that appears, you can change the party's active paradigm and also modify its deck. To do the latter, choose Customize. Select any of the 6 available slots, and you will have the option to edit the paradigm contained therein. You can also reorder the list to suit your preferences using /// and /. To change the party's active paradigm, select the desired one and press /.