You won't want to change the height. Once you fix that height, it may get rid of that text at the bottom that you don't like, but it also won't grow as comments are added. That would break the functionality of the module altogether. It's also against Facebook's terms to hide their little branding, but that's sort of besides the point.
As for the width, that can be configured in the Social configuration area of JFBConnect or in the module parameters for the Comments box. It depends on if you added that comment box or if it's being added automatically. That will hopefully help you narrow it down, but if not, let me know how you've added the comment box to that page, and we'll gladly help you get the width right.
Thanks,
Alex