Did you receive a W-2 or 1099 after you already submitted your return? Did you input incorrect information and need to fix it, but it's already been accepted? Once a return is accepted by the IRS, it is not possible to make any changes or correct any information online. If you answered "yes" to either question above, you'll need to amend your tax return.
Here's a few tidbits of information that outlines the amendment process.
1. Before attempting to amend your return, you need to allow your original return processing to be completed and any refund issued.
2. Amended returns (Form 1040X) must be filed as paper returns by mail (the old-fashioned way), and a copy of any form/schedule that has changed or was not included in your original filed return needs to be attached and submitted with the amended return. In general, these are mailed to the IRS Processing Center assigned to your State of residence. You can find that address by following this link: http://www.irs.gov/uac/Where-To-File-Addresses-for-Tax-Professionals
3. It can take 12 weeks or longer for amended returns to be processed. So if the amended return results in additional refund, please be patient. During filing season, amendment processing "takes a back seat" to the processing of original filed returns and is also subject to "backlog" delay. Oh, and speaking of refunds, the only option in receiving it is by check. No direct deposit option exists.
4. Be clear and concise in the "explanations" you must write as to why the change(s) were made. Vague statement(s) can slow down or halt processing if your explanation is not clear.
Below is a link to the instructions for Form 1040X for more information.