remove space on top of website

Hi, On the top of my website (inlog required for access) there is a big white space before showing the header. So on top of the browser/screen. I would like to remove that so that the header (on every page a different one) starts just slight below the borders of the browser. How can that be done? Other question: The width of my header is not the same as the width of the body text. How/where can I adjust that? Thank you so much, theme is wonderful! Eric