If you update your book that is already live, your book will go into review again to ensure it meets all the KDP guidelines. The manuscript (unless your manuscript changes the page count by more than 10%, you will need to create it as a new book listing), cover, publishing and territory rights, contributors, description, categories and other book details can be updated. There are certain changes that require you to publish a new edition rather than being able to update it. Like for instance the language, book title, subtitle, edition number, primary author and if significant changes are made to your manuscript, it’s considered a new edition and should be published as a new book. If your book is in draft and has not gone live you can still make these changes or updates before submitting it for review to go live.
To update your book:
If your book is in draft, it has not been previously published and doesn't have an ISBN assigned:
If your book has already been released, you can unpublish it so that no one can buy it but you cannot delete it from your bookshelf and the book will continue to be in the Unpublish status on your bookshelf. The detail page for your book will continue to be accessible on Amazon but customers won't be able to order new copies of your book, only used print books are still available on KDP via third parties. A book that has been unpublished is no longer available for purchase until it has been republished.