Review fare conditions found in your booking confirmation email or paper ticket sent to you by your airline or travel agent. The fare conditions will tell you whether a refund is possible, the time period in which you can cancel your ticket after the purchase, and if you will have to pay administration fees to cancel.
Gather your flight information and payment method (credit card or banking information). Contact your airline either by phone, or send in an online refund request via their website (most airline websites offer this service), or call your travel agent to begin processing your cancellation.
Prepare to pay a cancellation fee or an administration fee. If you did not buy traveler's insurance or Flight Guard that covers flight cancellations, chances are that you will have to pay a fee to cancel your flight and get a refund. In the long run, this is much better than losing all of your money.