This happens because every time a URL (web link) is shared on Facebook, Facebook caches (remembers) basic information about the page such as the images on the page, the title of the page, the description of the page. Then, when the same web page is shared (by you or someone else), rather than Facebook visiting the web page and retrieving the content and images again, it refers to its own cache (memory) from the last time someone shared that page.
Now, this works perfectly when the content of a web page does not change. But if the content does change, Facebook does not check for changes and continues to use the information from its cache as the preview.
How to clear Facebook’s cache
Fortunately, it is very easy to force Facebook to clear its cache and request the new content. Simply visit Facebook’s developer debugger
Enter the URL of the web page in question and hit the “debug” button.
Hit Scrape Again to preview the new content.
That’s it. Go back to your status update and share the URL, and you should see the up to date content.