you should remove a page from the website then server and sitemap need to re-index your website. otherwise, you can redirect your webpage old page to new page.
- Open your website in Google Sites.
- Click the page you want to delete. If you delete a page, you also delete its attachments, comments, and child pages.
- Click More actions Delete page.
- Click Delete.
It depends on the platform you created the site as well.
Weebly, Wix, Google etc... It will all be in the settings tab. Alternatively, ask customer support or seek the FAQ page