Go to Delta.com and click the "Itineraries and Check-In" link under the "Traveling and Check-In" tab.
Enter your confirmation number, credit card number or eticket number, along with your name, and click "search" to find your flights.
Click "Cancel your Flight" to receive a full refund on your credit card. Cancel you flight by midnight on the day after you've purchased the eticket to be eligible for a full refund.
Click on "Plan a Trip" under the "Planning and Reservations" tab on the Delta website to begin.
Find the "Best Fare Guarantee" page under the "Online Reservations" tab.
Click on "Submit a claim" to fill out the claim form.
Enter your personal information, confirmation number and dates of the flight you've booked.
Copy and paste the link to the site when you've found a better fare, and the amount of that fare, in the appropriate boxes.
Click "Go" to submit your claim. Delta will verify the claim, issue a refund of the price difference to your credit card and give you an electronic travel voucher within 24 hours.