I updated my published book, but when I download it, it's not changed. What's Wrong?
Note, this article has been superseded. The original information, published in 2018, is no longer valid.
Now, due to changes in KDP's policy, if you buy a copy of your ebook, after you publish it, and then decide that you're going to update it, you will not be able to obtain an updated copy on your Kindle device. yes, that's right, KDP will no longer 'push' a new copy of your updated file to you, the publisher.
While KDP did not announce this as a major change, the changed policy--along with their policy about updating purchasing customer's copies--is clearly stated on their HELP pages, here:
Although the title of that article originally makes it appear that you can "push" updated content--in short, you can't. Not unless KDP itself demanded that you make the changes, or that they were so significant that the original buyer would have had a disappointing experience. In short, what they are telling you is, "don't think that you can just update your ebooks willy-nilly; make sure that they are as perfect as possible before you publish!"
One can only presume that KDP was so overwhelmed with requests, for updated files being "pushed" to owner's Kindles, that they just got fed up. I do know that I've seen not one, but many publishers on the various Kindle and KDP forums nearly bragging about the fact that they've updated their eBooks 11, 15, 20-something times so you can see how KDP might have lost its sense of humor.
Nonetheless, you've been warned--don't assume that your Kindle ebook is like your 8th-grade book report, sitting on your computer in Word. You can't just willy-nilly update it and expect to see the latest and greatest on your device--you won't. Neither you, nor more importantly--your purchasers, either. So, edit, edit edit and proof, proof proof!
Superseded, old information, DO NOT USE or RELY UPON:
Unfortunately, just re-downloading your book won't get you the updated file. Why? Because Amazon customers can make annotations, bookmarks, etc., in their eBooks, and if a new version is "automagically" uploaded, over their existing, all that information is wiped out. Customers don't want that, not without choosing it for themselves. That means that you need to ask Amazon to "push" (that's the specific term to use) the new version to your "Content and Devices" so that you can upload it to your Kindle.
This also means that your existing buyers won't get the new, updated file, either. If you feel strongly that you want them to receive this, or have the option to receive it, you have to write to Amazon, or use their Contact Us page, https://kdp.amazon.com/en_US/contact-us and ask them to "push" the book to the buyers. They won't do this, just because you screwed up and didn't proofread! You have to explain to them, and make a compelling case, as to why they should notify the buyers that there's a new version, and make it available to them.
---end of superseded article---