A friend of mine, Tim Bruce, sent me a link to an article called, HowAmazon did everything wrong (but I still got to #1).
If you publish via Amazon - or if you're thinking of updating something you already have in the Amazon Kindle bookstore - you might want to read this article. It could save you some time and frustration. On the other hand, just reading it might change your mind about trying to update your book.
After you read the article, come back and tell us what you think.