Although many taxpayers equate "amending" with "changing," the word "amend" has a very specific, narrowly-defined meaning in the world of taxes.
In a tax context, to amend is to make changes to an e-filed return that has either been accepted by the government and processed, or a paper return that has already been mailed and processed. An amendment must be filed on a specific tax form created exclusively for that purpose (for example, Form 1040X is used to amend federal 1040 returns).
According to this definition, making changes to a return that hasn't been accepted or mailed yet isn't amending. For this reason, you can't amend an e-filed return that's in pending or rejected status. Please be sure that your return has been completely processed before filing your amended return (refund issued or the revenue agency put your tax balance due on their books).
If your return has been accepted and you need to amend it, we have instructions on how to amend.