Any time you "publish" to Premium it will cost points. That can be if you publish a chapter for the first time, or if you decide to publish a different version of the same chapter for people to review again.
You can also "edit" existing chapters, without it costing points.
Click on the menu at the top right of the home page and select Portfolio. It will provide a list of your works on the site. On the right hand side, click the Action menu for the work you want to update. You can choose Add Chapter or Edit, depending on what you want to do. Either choice takes you to a 5-step workflow to add or change your work.
Editing work allows you to incorporate changes for future reviewers to see, and they'll get points for the reviews. Those who have already reviewed the work will not get points for reviewing it again, unless you publish it as a new chapter, using the Add Chapter workflow. Add Chapter will cost you points.
If you want to publish a chapter to replace an existing one, follow the Add Chapter workflow, but give the new chapter a different version number (e.g., chapter 2, v2 instead of chapter 2, v1). You can then decide whether you want to leave the old version of the chapter visible for readers to compare before/after, or simply hide the old one. Be careful about deleting old chapters, since I believe the reviews on the old chapter disappear with it.
Hope that helps.
Dirk