Kindle Textbook Creator (KTC) outputs Kindle Package Format (KPF) files. KPF files are fixed (more on file types below). If you update an existing book using KTC, or switch to a different format when updating a book created in KTC, you'll find that the update is blocked.
 
  To update your book 

1. Make sure the title and author match exactly
   
2. Publish the new version as you normally would
   
3. Unpublish the old version of your book
4. Note the ASINs for both versions
   
5. Contact KDP Customer Support to link the two versions so customer reviews can be merged

Important: When you create a new ASIN, customers who purchased the earlier version will not receive this new version for free. They'll have to buy it again if they want the improved version. Your existing sales rank will not carry over to the new version.
 
KTC publishes textbooks in KPF, since fixed format files offer the best overall reading experience for textbooks. To update a previously published book that was available in a reflowable format, you'll need to publish it again, and the two versions will be linked. This way, you can preserve your customer reviews—the update will be a new version of the same book, rather than an entirely different book.