Finding and editing a page
All your pages are accessible from the top left corner 'Page' next to the 'Add element' button. Clicking that button will reveal all your site pages.
Find the page you are looking for, and click it once to open that page. Once you have, you simply need to hover over or click on any part of the page that you want to start editing.
And of course, don't forget to save (top right corner).
To learn about editing specific elements on the page, click here.
This help video shows you how to find and edit a page: