From the page editor
To rename your page from the editor, click on the 'Settings' icon in the top left of the canvas. From here you can overwrite the page name. The name will be saved automatically.
From outside page editor
To rename a page from outside the editor, navigate to the your websites index page (see example screenshot below) and click on the 'Page Settings' icon to the right of the page you want to change.
From the Page Settings you are able to change the name of the page. Make sure you also change the URL name to match the name of the page.