Answers from another Blurb author:
1) I could not find this option. I upload my books as PDF files and check them out with the Blurb preview function. Does the software that you use to make the book have a Save As PDF option? This is what I use to convert my books into PDF.
2) I have asked Customer Support about this and they said it is not possible. Their suggestion was to delete the earlier version of the book and upload the updated version as a new book. This is quite annoying and time consuming as one has to start afresh and add all the data again. This a lot of trouble to go to just to fix a typo or page layout problem. Remember you must buy a paper copy of your updated book within 15 days or else it will be removed from the server/bookstore!
Other on-line publishing websites allow any number of book edits for free.