How do I update my theme’s meta tag information that appears in Facebook, etc?

There are many ways to do this, these easiest of which is installing the Yoast SEO plugin and adding your information, as needed. Once you’ve added this information, you’ll just need to run your site through the Facebook Debugger tool as many times as needed before the information is updated to your satisfaction. 

Here’s a great link to an article that will walk you through this process in more detail: