To get your Nook for PC...click on any of the ebooks...then on the upper right you should see the words--
"Available on Nook devices and apps (?)" Click on the question mark. A list will come up. There you will find the Nook for PC to download. Hope this helps.
You should be able to upload your new version over the old one. Just upload the book again and it will overwrite the old one. Then save. Unless save isn't working, which happens sometimes. But give it a try.
Like I said, when I try to add the new file I get a "file allready loaded" error.
Back to home grown work arounds I guess.
Alos it's nice that BnN does not send you back to where you were after you sign in. So you have to figure out how to get back there on your own.
I'm seeing lots of little things like this , that make me wonder how well run BnN is. Or at least their digital section.