You can only edit the text above the post image. NOT the image or text below the image. Ifyou need to edit the image or text below the image, you will need to delete the post and repost it using the 'Share' tool found in the 'Edit' section for the landing page.
The video below also shows how to set the image and the text below the image!
🏅 Facebook & LinkedIn
Click the 3 horizontal dots in the upper right corner of the post, select 'edit' from the drop down and edit as needed.