Wp admin url not working

Hi…complicated story….setup wp on a shared IP address….so I could move my entire site and data and confirm it was working before deleting and transferring the DNS from the old server to the new one. All was well until support changed the DNS pathway. Now, when I try to login to admin( the blog is visible on the site and working) I get not found as the pathway is no longer correct. How do I correct the pathway without losing the entire setup and all the posts? I tried install.php but it said everything was already installed….any help appreciated.