Facebook display an unwanted preview of my image and text.

The easy way to manage the site preview that shows up on Facebook is the free plugin Yoast SEO. With this plugin, you will be able to display what you want onto the preview and it will help you to improve your site’s SEO. 

  1.  Download the Yoast SEO plugin.
  2. Install and activate it on your WordPress site.
  3. Edit your homepage backend and look for the Yoast SEO setting.
  4. Click on the social icon

  1. And fill the title and description fields. You can also select a new preview image

See the full Yoast SEO Documentation here