Every organization will have a default currency set on their Organization Info page. Set this to your preferred default currency, as shown:
For each donation campaign, you can also change the currency to be different from your default currency. To do this, click the edit icon by your campaign.
Click the 'Amounts' link under the 'Your Donation Form' header to set a new currency on your form. You can also enable our multicurrency donation form feature to add multiple currencies to your form.
Click update or next for the changes to go live.