Hiya all again,
I am writing this tip or trick as there is someone there asking for one. It it not really simple but not too difficult too.
The modified forum menu will look like this:

Basically, we need to open our index.css and make some changes.
1. For moving the curve body a little bit lower, find:
body
{
background: #E9EEF2 url(../images/theme/backdrop.png) repeat-x;
font: 78%/130% "Verdana", "Arial", "Helvetica", sans-serif;
margin: 0 auto;
padding: 15px 0;
}
Change it to:
body
{
background: #E9EEF2 url(../images/theme/backdrop.png) repeat-x;
font: 78%/130% "Verdana", "Arial", "Helvetica", sans-serif;
margin: 0 auto;
padding: 45px 0;
}
2. To move current menu to very top of your forum, find:
#main_menu
{
padding: 0 0.5em;
float: left;
margin: 0;
width: 98%;
}
Change it to:
#main_menu
{
padding: 5px 5%;
float: left;
margin: 0;
width: 100%;
height: 20px;
position: absolute;
top: 0;
left: 0;
background: #eeeeff;
}
3. Lastly, you want to clear the empty spaces under the upper section, so find:
#upper_section
{
padding: 5px;
margin-bottom: 1.5em;
}
Change it too:
#upper_section
{
padding: 5px;
margin-bottom: -40px;
}