Nick here from Shopify.
You are able to change the currency from your store if you wish. This is something you would need to contact the support team directly to do. Only after you have launched your store and have made sales, can you make the change. You can contact Shopify Support here to change your store currency.
You can see the help guide Shopify has about this here.
Hi @Kath08 !
As you want to switch the currency in your store, Transcy is the most suitable choice that can assist you with this. This is third-party app featured with currency converter and language translation. Particularly, Transcy can set up your store up to 167 currency units and can even auto detect the location of store's visitors to display the friendly switcher.
Moreover, Transcy is available with FREE plan, so you can take free ride without being charged. Hope it can help!