Yes, you can if the payment has not already been processed. You can modify or delete the EFT up until 2:00 PM (Mountain Time) the business day before the settlement date.
To view the status of your EFT payment, click here or you can click on "Payments" on the top menu, and then click "View All Payment Options". From the Payment screen, click on the "View or Edit a Pending EFT Payment" link. If your payment has not already been processed, it will be listed on that screen.