The theme includes a currency conversion feature which lets you provide a drop-down selector that lets customers view your prices in different currencies. Their currency selection will be stored in a cookie and used again on their next visit to your store.
Exchange rates used by Shopify are refreshed twice a day based on the rates at XE.com. Although rates are automatically scheduled to be updated at 00:00 GMT and 07:00 GMT, the updates might take place up to a couple of hours after their scheduled time.
No matter what currency you show on store pages, Shopify will always process orders in your store's operating currency.
To enable currency switch, go to Theme Editor > Settings > Header & Mobile Menu and click on 'Display Currency Switcher' to make it active.