While editing the site, click on the pencil icon to the right of the menu. Select 'Reorder Menu’.
You also have the ability to move pages to different positions on the menu, apart from the homepage which always remains in the main menu. For more information on homepage features, please refer to this article.
To move the position of a page, hover over the desired page item until the edit pencil appears. Click on the edit pencil and then, click Move.
To re-position your page under a different sub-page, click the 'Position page under' drop down button and select the page.
To change the order of your pages on the menu, click the 'Position' drop down button and select its desired position.