Jim – the entire code snippet that Stephen provided above would go in your theme’s functions.php file. This assumes you have FTP access to your site’s files. It would be located in the wp-content/themes/[your theme]/ folder.
Jim, Kym is right, but you can also use the simple built-in editor in WordPress to copy and paste that code snippet I listed above into your theme’s functions.php file. Look under Appearance>Editor . Then, look for the functions.php file in the list on the right side of your screen (making sure your active theme is also selected first in the select box to select the theme to edit). Really best to have a child theme for that so that you can still update the parent theme without wiping out that added bit of code. In that case, be sure to select the child theme first, and edit its functions.php file.