Basically, while sharing a link for the first time, the object debugger stores the meta information in its databases so when you share again, instead of debugging the URL, it takes from its own database. So a shared URL even upon changing the description/image/title, does not get affected sooner.
So, to overcome this and see quicker results of custom description/ changing image/ changing blog or post title, facebook has a facility called the Open Graph Object Debugger.
- Go to the open graph object debugger, https://developers.facebook.com/tools/debug/og/object/
- In the Input URL box, provide your post URL
- click on Fetch new Scrap information
- When this is done, try sharing the post on your face book wall.