If the book is showing as Live, it's already published. Do you mean you need to make corrections? If so, you upload a corrected file over the original file, not as if making a new book, do the Save and Publish thing again, and then you have to wait another period of time for the updates to be fully accepted. While the book is publishing, you won't be able to do anything else until it's Live again. This is why it's wise to make sure the file is correct before you begin to upload; though mistakes can happen it's best to minimize them as much as possible due to the length of time it takes to get the file done.