Should/Could I change the title of a book when republishing it?

Hi all
I have a question and thought I'd ask all you KBoarders as I'm unsure what to do.
I have a book, a pre-apocalyptic end-of-days saga, A Time of Demons that will come back to me after 5 years from my publisher and I'm going to self-publish it in June. With the publisher it never sold well though the reviews were good. I believe it is one of my best novels so I want to relaunch it the in the best way I can. Of course I'm changing the cover (I have a great cover artist Dawne Dominique) and because a lot of people didn't like the cover or the title I was also thinking of changing the title to A Time of Demons and Angels, perhaps with the "and Angels" smaller below the main title as almost a sub-title because I've also been told the original title doesn't really show an end-of-days theme that well. It has demons and angels in it. Is this ever done? Would I have any problem with Amazon, B&N, Nook, etc. by doing this - changing a title on a book that was for sale there for 5 years under the original name? Any other thoughts on if I should do this or not? Help!