Amendments (1040x and your state's equivalent) are not the easiest things to fill out. There are two basic steps (if you aren't using software to do so). Redo the 1040 to include the changes you are making and then reflect those changes on the 1040x. Any associated supporting forms for the 1040 that need to be modified also need to be handled. Attach the 1040x, 1040, and associated documents and you have what needs to be submitted to the IRS. A similiar thing often has to be done with the associated state returns.
The dollar amounts for EIC can be found in the 1040 instructions based on filing status, income, and # of qualifying children for EIC.
Adam Accountant Wilmington NC