In this documentation you will learn
Admin Panel Left Menu
How to manage currency in cart21 shopping cart?
E-commerce > Currency ( /admin/currency ) in this section all currency registered to system is visible as a list. you can add or edit a currency in this section.
Currency List Section
Currency Form to add or edit a currency
How to set a currency as website default currency from settings
Go To admin panel > Left Menu > SETTINGS > Website Settings
as shown image below all currency will be visible in currency select box and then select the currency you want to make default.