The theme templates define what is displayed on each page, such as the title, content or extract, and other metadata. You can edit the theme by peeking into the wp-content/themes . The list of folders there is a list of themes installed and you'll have to modify the one being used by your current setup.
Ideally, you would want to do this with a page template at. Here's a good explanation of page templates:
It is possible to use plugins to get WordPress to go to a different page defined by the plugin, but that isn't versatile (a theme may want to override it, but it can't!) - the theme ought to handle the page layout, not the plugin.