there are some guides in the first few links on google
i tried some but couldn't do it.....
hmm, try this http://koyukiya.tumblr.com/ebook
you can scroll down to the extraction part, since you already have an ebook. Goodluck! (Her menthod should work, at least it did for me)
Also, I'm sorry for my first reply. I got a bit annoyed because a lot of people here don't check/try before they ask..
anyone know how to download/extract a manga/book from Amazon and Kobo please please it's urgent!