There is a way to change the widths, but it means modifying the core theme files….when this has to be done, it’s recommended to use a child theme to override core theme files (as suggested by WordPress). This allows you to keep the parent theme up to date. In doing so, you would copy the necessary files over into the child theme (has to be active) and then you can make the modifications. If you are using the left layout, you will need to do this for these:
The widths are in relation to the “responsive” framework and uses a class called a span, followed by a number. Basically this framework is based on a 12 column layout, so a span8 on the main content container means it takes up 8 columns in width. The sidebar uses a span4, so together they add up to 12 columns in width.
In the source code of the above files, you need to change the span8 to a span9, then the sidebar from span4 to span3. When you take away from one, you have to add it to the other and vice versa. So for you, span9 + span3 = 12 column width in total.
You will have to do this same process for the page files as well:
As for your second item, are you referring to the WordPress header function under the Appearance menu? I just tried this on my local test site and was able to get it to show on the front page. You may want to try once again but it it’s not working, I may need access to your admin (and site) to see what is happening.