Hi RR, very easy once you know the steps. First sign into your account. Next click on "change flight". You will be asked to provide the confirmation number and first and last names. Choose your same flights or any two flights for that matter (assuming flights are cheaper). Complete the transaction and you will see the flight credit. I print out the credit before leaving that page. Confirmation number will remain the same. To use credits in the future you need the confirmation number.

Takes no more than 2 minutes as you do not need to input any information. These days with higher flight fares I book early and often, same way they vote in Chicago.