Get the Right Forms
Use form 1040X "Amended U.S. Individual Income Tax Return" to amend your tax return. You will need a separate 1040X for each year you are amending. Pay close attention to Part III, "Explanation of Changes," as it's your opportunity to tell the IRS why you are filing an amended return.
Gather the Attachments and Mail It In
You'll need copies of any schedules affected by your changes. You can also provide a copy of your 1099 if you've received it and income tax was deducted. Once you have your documentation, mail it to the appropriate IRS location as listed in the Form 1040X instructions. Mail each amended return in a separate envelope. You can check the status of your amended return by using the online "Where's My Amended Return?" website.
Don't Forget Your State Taxes
Changes to your federal tax return may change your state taxes. To get more information, contact your state tax agency.