From time to time, the developer or publisher of an iBook may update it to correct errors, make it compatible with a newer operating system or otherwise fix it. There is an easy way to determine this and get the updates. Here’s how.
- On your iOS device, tap iBooks. If a book is open, tap on Library at the top left to close it.
- At the bottom right you should see “Purchased” and there may even be a red badge with a number in it showing you how many book updates are available.
- Tap on Purchased. Then, tap on Updates, in the middle at the top.
- Now, tap on the individual books to update by tapping on the blue update button on the left or tap on update all to update all of the books. You should use Wi-Fi as some books may be large and the process of updating may take some time.
You should see something similar to the image below when you are in the process of updating.
After the updates, you can go back to reading.
iPad Notebook 
Hi
do you know how to determine what changes the update of an iBook includes? Is there anything similar to the “What’s New in Version xxx” section of the App Store?
I would think the author or publisher would indicate what the changes were. If not, try emailing them and ask.
I’m wondering if this feature applies to a “revised edition” of a book. E.g. if I purchase the 3rd edition of Wayne Booth’s “The Craft of Research” will the 4th edition of the same book appear as a free update, or will I need to purchase it as a new book?
It may also depend on whether the author is charging for the update. A new edition may cost money. Revisions to an existing may not.