Theme: Twenty Eleven, Text Width used, Banner Width

Hi All,
Two questions in one really…

I am using the Twenty Eleven theme, (largely because that’s what the how to book I am using recommends!)

It seems to be going OK, and meets my needs, but there’s one aspect I don’t like, which I want to change.

The text does not use the full width available in the frame it is displayed in, i.e. it does not go out to the full width of the banner header image across the top. This wastes quite a bit of screen space, and I’d like to make it wider.

Is this possible?

Closely related, (at least in my mind!), I’d like to use a different size for the banner across the top – again a larger one would make better use of a large screen. Everything seems to scale nicely for smaller screens, so I don’t anticipate any problems there.

Can I use larger banner images?

Thanks,
Nick