Twenty Fourteen, narrow content

Hi all,
I just installed TwentyFourteen, and I like the layout very much. But I am confused what to do with the empty space on the right of the screen and left and right of the text. Half of the screen is empty white or empty grey.
And: couldn’t one format the text to be displayed in a wider area?

<----------------------------total screen width ----------------------->
_____empty white                              empty white empty grey
mnue|----------|texttexttexttexttexttexttext||----------|---------------

How can I widen the text area and how can I use typically the empty grey area on the right hand?

Thank-you all!

Regards CJC