Decreasing margin above header

I am a newbie using twentyten and would like to reduce the space between the top of my browser and the header. I don’t use the Site Title or Tagline and have been trying to find out how to reduce the inch or more from above the header. I have not modified twentyten and the code I am looking at is pasted below:
/* The main theme structure */
#access .menu-header,
div.menu,
#colophon,
#branding,
#main,
#wrapper {
margin: 0 auto;
width: 940px;
}
#wrapper {
background: #fff;
margin-top: 20px;
padding: 0 20px;
}

If someone can tell me how to make a change that will fix this I can create a child theme and do so.