If your tickets are non-refundable (which 99.9% of tickets are these days) then you can't cancel your booking, but you can CHANGE the flight for a fee (usually $50 per ticket on Delta, $25 on Song).
Urgh! How frustrating! I was able to save about $30 on my flight to FL since it was booked through SW. I could have saved another $60 if I could have cancelled the Delta Flight. Who would have ever thought there'd be a $40 flight?????