The site provides two ways to handle this:
1. Edit (overwrite) the existing chapter by simply replacing the contents of the chapter. This allows you to put up the changes for those who haven't yet read it, avoiding the hassle of everyone telling you about the same errors. You do not require points to edit an existing chapter, but it also won't appear on everyone's home pages as a new chapter, and it won't pay points to those who already reviewed it. The system sees it as the same chapter, albeit with different text.
2. Create a new chapter with an incremented version number. This requires points and will appear on everyone's home page as a new chapter, and will pay points to everyone who reviews it. You then have the option of making the old chapter inactive (invisible), which is usually advisable to avoid confusion. One time when you may want to leave the old chapter active is if you want people to be able to compare the old and the new. Even though an inactive chapter is not visible to others, you still have access to it and to all of the reviews associated with it. If you're completely done with the old chapter and its reviews, you can also delete the chapter, which will eliminate the old reviews with it.
Most of the above steps you can find by clicking around inside your portfolio from your menu at the top right of the home screen, and from within the chapter view of individual chapters (i.e., where you normally go to view your chapters). One word of caution, there are two ways to edit a chapter when you're viewing it. The white edit "button" will take you to the 5-step publish wizard that you're already familiar with. From within there, you can do anything you like (simple edit, add chapters, publish, make active/inactive, delete, etc.). In addition to the edit button, there is also an edit "link" further down the screen on the chapter view. The edit link is a shortcut to editing your existing chapter text without replacing the chapter (i.e., option 1 above).
Clear as mud? Feel free to post back if you need more help.
Dirk