Check your final tax form (you can download or print a copy from the web site if you filed online).
If you do not have a schedule A, then the interest you reported made no difference and it will probably not help to change it unless it was a huge error.
If you do have a schedule A then your mortgage interest is on line 10 and 11, and your total itemized deduction is on form 1040 line 40. If you reported too much interest, you much amend to report the lower amount and pay back any extra tax owed. If you reported less than the correct amount, then it is your choice whether to amend. You should expect to get between 15% and 25% of the interest difference back as an additional refund. (In other words, if your interest deduction was $100 too low, and you amend, you will probably get back $15-25.)
If you originally claimed less than the correct amount of interest and decide not to amend, you can't claim it next year instead. You claim your 2015 interest on your 2015 tax return, or never.
For amending instructions start here,
https://ttlc.intuit.com/replies/3288565
