the images are in the the templates/jw_vividdesign/images/ directory
Depending on your hosting permissions you might not be able to overwrite this with FTP, you may be able to set these files permissions to 777 and then overwrite them. If not you can download joomlaXplorer (
extensions.joomla.org
) and install that component. This component will let you modify the permissions or upload a new file etc.