If you wish to make additional customization to any theme you download, you can alter the overall layout by editing the main template files: home.html, content.html, and search.html.
To create language-specific customizations to any theme, copy any main template file (e.g. "home.html") to a language-specific template file by added an underscore followed by the language code "_{language-code}" (e.g. "home_es.html").
To customize the look of individual components under any theme, copy and default component HMTL file from the main "comp" directory in the root of your WPM installation (e.g. "comp/simpletext.html") to the "comp" folder of this theme (e.g. "tmpl/{theme}/comp/simpletext.html") and edit it as needed.