Are you referring to the featured images? Are you sure you want them 960px wide? They would take up the full width content (if you also have a sidebar).
Featured image size is configured in theme settings, under (!) Featured Image Settings.
However, changing options there will have no effect for files already uploaded in your library, just for future uploads.
For existing files you’ll need to use a thumbnail regeneration plugin to re-create the crops/resizes at the new size.