Preparing an amended return isnt difficult.

Open the return.  Go to Forms and choose 1040X.  On the 1040X, mark the year box at the top of the screen.   If a state is involved, go to the state return and do the same thing, open their amended return for mark the correct year at the top.

Now go back to the federal return and make the changes you're amending for, and scroll to the bottom of the 1040X and type in your explanation of changes. Go back to the state and make sure the explanation description is filled in there as well.