There is no extra fee to file an extension, but the extension is only to file the return, not to pay. If you don't pay your taxes due by 04/18/2017, you are subject to a penalty. So you should make a payment with your extension if you think you'll. owe.
To file an extension, go to Federal Taxes and choose Other Tax Situations. Scroll Down to Other Tax Forms and choose File an Extension. See the screenshots below.