We can add/remove currencies in Prestashop by doing the following:
Go to admin, select Payments and click on currency link, you will get a screen like this:
Click on Add New button to add currency if you need. In order to remove currency click the check box of the currency and press the delete selection. If you want some currencies for using later, better don’t delete it, click the check mark to disable it, later if needed you can enable it by clicking the X button.