Can I change my federal income tax return?
Once you have dropped your original income tax return in the mailbox or sent it off electronically, you can no longer change that return. (One exception: If your e-filed tax return is rejected, you can make changes before sending it in again.)
If you want to make changes after the original tax return has been filed, you must file an amended tax return using a special Form called the 1040X, entering the corrected information and explaining why you are changing what was reported on your original return. You don't have to redo your entire return, either. Just show the necessary changes and adjust your tax liability accordingly.
You generally must file an amended return within three years of the date you filed the original return or within two years after the date you paid the tax, whichever is later.