To replace content, simply upload your file as normal and the new file will overwrite the existing file and be available to approved readers very quickly—there is a very short “moment of conversion” that likely won’t be noticed unless someone presses Download during the exact moment the file is being processed.
You can always preview the new file (and we encourage you to do so!) using the Preview link. Details here.
Publishers and authors who sign up per title should follow the same process unless the file is over 24MB. If your file is over 24MB, please email it to firstname.lastname@example.org with the subject: Update content file for ISBN, TITLE.