You can open your filed return and change it, view it or do anything with it. There is only 1 data file, the .tax2011 file. In the Desktop program you can have unlimited files. Maybe you didn't save the filed one or can't find it. Search your hard drive for all files ending in .tax or .tax2011.
If you are using the desktop program you should have both the pdf AND the .tax2011 files. In fact to amend it you need to use the .tax2011 file (the original one that you efiled).
You shouldn't change anything after you mail or efile until you start the amended return process. Also you have to wait until you get your first refund or your tax due payment has cleared your bank.
The amended return is form 1040X and can only be mailed (not efiled) and will take 8-12 weeks or more to process. And they only send checks for amended returns, no direct deposit. You should also wait to amend your return until you get your original refund or your payment has cleared because the IRS might adjust your original return.
When you go through the amendment section it asks you how much you paid or got back on the original return so be sure to enter it. Then the amended return will only show the difference you get back or need to pay. You can confirm this by printing your amendment and looking at the 1040X. Line 17 should be your original refund amount and line 20 should be your additional refund. If you paid on your original return it will be on line 15. If there is an amount owed with the amendment, it will be on line 19.
If you don't see a button for Need to Amend a Filed Return? on your home screen then you can get to it here. Go to: Federal Taxes -or- Personal (for H&B) Other Tax Situations last section, Other Tax Forms Amend A Return - Click the Start or Update button