You have to fill out an amended return on paper, using Form 1040X, if you need to change your filing status or if you have changes to your income, deduction or tax credit information. The form is available online at the IRS website. To get your refund, this needs to be done within three years after the date you filed the original return or two years after you paid the taxes owed, whichever is later. If you are filing to claim an additional refund, the IRS prefers that you wait until you get your original refund before filing the amended return. The address you'll send it to depends on your reason for filing, but can be found on the 1040X instructions. Normal processing time is eight to 12 weeks.
When No Update Needed
When you file your tax return, you sign a statement that indicates it's accurate to the best of your knowledge, under penalty of perjury. That doesn't imply that it has to be perfect, however. For example, you don't need to file an amended return for math errors since the IRS will correct them. You also don't need to file one if you neglected to include a W-2, 1099 or a worksheet. The IRS will either process the return without those documents or send you a letter requesting them.