What does it take to leave a hybrid publisher?

At the time I chose to work with a hybrid publisher a few years ago, it was a satisfactory option for my situation. It wasn’t a uniformly bad experience, but it left me with too many pieces I wish I could control. Now, I am writing a second novel (loosely in series with the first) and am better positioned to self-publish. So I’m contemplating getting the first one back from the hybrid publisher before my contract with them renews.

What do I need to know and do to self-publish the first book? What happens to the ISBN? Is it even advisable for me to make this move? (I know hybrid publishing is @Thomas Umstattd Jr.’s most derided option, and that has kept me from saying anything here for a long time. Yes, I’m the black sheep of the ONM family.) But I’m back now, munching on crow and asking for help, hoping there is a way to become the publisher of all my own books from this point forward.

Ideas?