It depends on the rules for the fare you originally booked. Depending on the fare, you may have to pay a fee for any changes, including application of a fare reduction. Typically, for heavily-discounted fares, that would nullify any benefit you would gain from such a small reduction in your fare.
On the other hand, if you purchased full-fare coach class (Y fares), then the airline will apply the fare reduction for you without a fee.