Hi, Glenda. Your question is complicated, and nobody can give you legal advice for your situation in a public forum, but maybe this will help you understand some of the issues involved.
If you have the rights to your book--if, for example, you received a termination letter from your publisher--you may freely submit that book, as is, wherever you please. You don't need to change anything. The publishing rights belong to you, and you may offer them to other publishers. Whether or not it's a good idea to do so is another matter. If your book was previously published, any other publisher will want to know how it sold, and if it did miserably, that will probably count against you. Also, you're probably a better writer now than when you first wrote the book, so it no longer reflects your skill level and ability. Given that, you may want to rewrite the book, or even put it aside and work on a better one instead.
Unless you are self-publishing, don't bother registering the copyright on your book. Real publishers--not vanity outfits like PA--do that for the author, in the author's name. (Don't believe the crap some scam publishers tell you about how "all those other publishers" take your copyright. Not true.) In the US, copyright exists from the moment of creation, not from registration.
If you have not received a termination and reversion of rights from your book's publisher, your situation is trickier. You cannot legally offer that book to anyone else. You may write something very like your book and sell that, but you cannot just make a few small changes. Determining what changes are enough to make it a different book is complicated and not an issue I'm even going to touch, because there are legal issues involved and I'm not an expert.
Reading through some of the threads here on AW (like How Real Publishing Works, which is at the top of this board) and searching the PA threads may give you more information. Good luck!