People with admin or maintainer permissions for a repository can delete a GitHub Pages site.
GitHub Pages is available in public repositories with GitHub Free and GitHub Free for organizations, and in public and private repositories with GitHub Pro, GitHub Team, GitHub Enterprise Cloud, and GitHub Enterprise Server. For more information, see GitHub’s plans.
If you want to remove the current deployment of your site but do not want to delete the site, you can unpublish your site. For more information, see Unpublishing a GitHub Pages site.