You'll need to act quickly. The due date for filing an amended return is generally the later of (a) three years from the date you filed the original return or (b) two years from the date you paid the taxes due, so it may be too late to amend the 2013 tax return. You can get the 2014 TurboTax software here: TurboTax Prior Year Personal Tax Products, but again, time may be running out to file the amendment.
(Note: TurboTax 2013 software is not available, but the IRS has Prior Year Forms and Instructions. If you choose to go this route, this document will help you get started: How to File an Amended Return with the IRS.)