Editing general site information is simple in Google Sites. On any page, click onto More on the top right corner (or M on your keyboard) then click onto Manage Site (or G + P on your keyboard). You will then be redirected to Google Site's site management system.
On this page, you will be able to change your site's name, categories, and description just as you did when you first created the site. You also have the option to configure search options, see site statistics, change the site's language, and more.