If you post a link to a website, Facebook generates a selection of possible thumbnails from the existing links. If you are not satisfied with the selection or the correct image is not displayed, there are two solutions.
1. if the image on the website has already been corrected, but Facebook has not yet adopted it, you can use the Facebook debugger to re-read the corresponding website link.
If there are still problems after that, you can use the WordPress plugin Yoast, for example, to set a Facebook image for the corresponding subpage in advance.
2. if the post was already posted, this must not necessarily be deleted. If you click on the post in the upper right corner via the arrow, there is the option to have the preview image re-imported as well.