I'm using the Wordpress CMS. I don't have access to the theme's code etc..
So how do I update the opeh graph tags? I'm mainly looking to add an image to go along with it, as it's using the default WordPress image when I share on Facebook.
Questions on WordPress Answers are expected to relate to WordPress within the scope defined in the FAQ. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about closed questions here.
Do you have access to (installing) plugins? There are several plugins that lets you add the Open Graph tags: http://wordpress.org/extend/plugins/search.php?q=open+graph
Here's the way I did after finding a solution via google. This seems to work an pulls an image based on the featured image set on a post. If it is a main page or a post/page with no featured image, there is a conditional statement which allows you to set a static image.
Sorry, just noticed you said you didnt have access to the code. I guess a plugin is your only route. If you can get access to the header, you can try my code snippet above.
Yes, a plugin that can do it: http://wordpress.org/extend/plugins/facebook-open-graph-meta-in-wordpress/
And more info (another way of) doing this on this code route: http://www.wpbeginner.com/wp-themes/how-to-add-facebook-open-graph-meta-data-in-wordpress-themes/