To change the currency on your store visit your general settings page here: http://my.cratejoy.com/settings/
You can also get there by clicking "General" under the settings tab.
You will see a dropdown labeled "Store Currency". Choose the currency your store will use and save. Thats it!
Keep in mind, the only restriction on this is that you cannot have any active subscribers on your store at the time you want to change your currency.