You can unpublish your GitHub Project Pages site if the content is no longer relevant or you no longer want it to be publicly available.
To unpublish your Project Pages site, delete the
masterbranch in the project repository where your Project Pages site is published from. For more information, see "Configuring a publishing source for GitHub Pages" and "Creating and deleting branches within your repository."
If there is a custom domain enabled for the site, update your DNS settings. For more information, see "Using a custom domain with GitHub Pages."