I have tried 'Update existing Facebook link' as well as delete the post directly and post it again but the image size is always the same.
You haven't answered my question about the none option on the AL2FB post meta box. Your FAQ says that FB doesn't allow posts without images. If so, what is the purpose of that option? Also, there are only two options on the meta box, none and the square thumbnail. These do not tally the options available on the plugin settings page. Where is the small and large options?
Finally, I can see that even if the square thumbnail image is selected the image displayed on FB is a small version of the landscape featured image.
In short as far as I can see I cannot make the images to change size whatever the settings I used. I tried on a totally fresh post and got the same result.
PS. I appreciate your prompt responses to help me to diagnose my problem. Thank you again.