If you need to make a change or an adjustment to a tax return that you have already filed then you will need to file an amended return. This can be done by filing Form 1040X.
Form 1040X
This form is officially called the Amended U.S. Individual Income Tax Return. Form 1040X should be used only to correct filed forms 1040 or 1040EZ. You can still file an amended return if you filed electronically.
Important Things to Remember
If you used an online tax preparation service then many of the errors that can cause you to file an amended return can be avoided. Services such as TurboTax Online offer step by step support to ensure you are entering all of your information correctly and that you are getting all the deductions and credits you deserve.