you might wanna check skin/vivid_dreams_aquamarine/css/altskin.css and edit the size of
#header .logo a img
Code:
#header .logo a img {
height: 54px;
width: 345px;
}
change to
Code:
#header .logo a img {
height: 100px;
width: 272px;
}
*You can always use
Firebug to see which css file to edit