I have four poetry books and two nonfiction books I have self-published but now I have removed them from the web so I can traditionally publish them. Is there anything I need to do? Can I keep using the ISBNs or do I have to change my titles to separate from the old ISBNS. I am just all confused on this matter.
When you create a contract with a traditional publisher, they will tell you what to do. Almost certainly they'll want to use their own ISBNs.
As for the ISBN itself, it's done with.
Can an ISBN be reused? No, once a title is published with an ISBN on it, the ISBN can never be used again. Even if a title goes out of print, the ISBN cannot be reused since the title continues to be catalogued by libraries and traded by used booksellers.
If you'd like ISBNs to use on new self-published titles, you'll need to purchase them fresh.
This is the least of your problems. The hard part is finding a publisher who is interested in publishing your books. Don't worry about it. When you find a publisher, they'll deal with things like ISBNs. It's not your problem.
Once you find a publisher, they'll assign their own ISBNs. You're old ISBNs will simply be dead. Whether the book is then published with the same title or a new title is between you and the publisher. There's no reason why it can't be. Books are republished with the same title and a different ISBN all the time.
You could say that as far as people in the book industry are concerned, a title does not identify a book. An ISBN identifies a book. This is because books can be published in different formats, like paperback and hard cover, with the same title. They'd have different ISBNs. Books that have entered public domain may be published by different companies with the same title, but again, they'll have different ISBN's. And occasionally, two books will be published with the same title but that have nothing to do with each other, it's just coincidence. For example, there's a book titled "The Stranger" by Albert Camus, and another book that as far as I know is a completely different book by Greg Van Arsdale and another by Harlan Coben. (I read the Camus book many years ago. I just found the other two searching on Amazon, I have no idea what they're about.)