To change the currency settings, from the store dashboard go to:
> Store Settings > Store Settings > Currencies

From with this page you can change the 'System currency', 'Default display currency' and 'Optional display currencies'.
*Never change the 'System currency' from 'United States Dollar (USD, $)' as this can interfere with the 'Markup Rules'*
*Underneath each of these settings is a description which informs you of what they each entail - please read them carefully*
(*Don't forget to click 'Save Changes' after making alterations*)