In order to change the currency you will need to go to your Settings page.
Once there, you will want to select the "Point of Sale" option from the list.
After that a new list will appear, and you will want to select "currency".
Click on the "what currency do you use?" and drop down list will open. Then you'll be able to select the currency you would like to use.
Hit the Save button right underneath.
Step by step video: