If you have modified the flipbook and want to reupload it online, it's quite easy to fulfill this.
Click Upload Online button in the main toolbar after you modify the flipbook, you can revise the descriptions if necessary. Tick Override an existed book, and then click Publish.
Step2. Select a host item to be overrided.
Choose the previous flipbook you want to override and then click select, your new flipbook will override the previous one.