Andrzej,
The Send button should be using the Open Graph tags that are set on the destination page of the Send button. We've seen that this isn't always done properly by Facebook, but if you haven't already, please make sure you've enabled Open Graph on your site (in the JFBConnect Social area) and set tags on your pages. If you need more information on how to do that, let us know.
Once set, you can use the tool below to check what Facebook sees as the Open Graph tags for the page:
developers.facebook.com/tools/debug
The information shown there -should- be used in the Send button, but like I said, Facebook sometimes ignores that data.. and we don't know why.
Hope that helps,
Alex