A little while ago I came across a handy little guide that explained how to return a Kindle library ebook before the time was up. I found this detail a little surprising becuase I didn't know you could return them early. In fact, I double checked Amazon's help pages and it's not mentioned.
Weird. In any case, I figure that if I didn't know about it and i cannot find the info then it is worth a post. So here is a video and a slideshow. The first was made by King County Library System and it shows how to get the library ebook. The second was made Wake County Public Libraries and it explains how to return the library ebook (it's an option on the "Manage Your Kindle" page).