You can hit ctrl + shift + i to open the developer tools and switch to the Elements tab to see the current state of the DOM. You can then change things to apply to the page.
Or, you can switch to the sources tab, right-click on "index.html" (or any other page for the site) and choose "override content" and pick a folder to store the edited file. You can then edit the source and reload the page and your changes will be there. And, you can right-click and choose to save your changes to an HTML file wherever you want.