Go to <Design><Template Designer><Advance><Add CSS> and paste Code
Use this code. I'll assure you it will work
/* decrease gap */
#sidebar-left-1 {
margin-right:-2px;
}
.column-right-inner {
margin-left:-15px;
}
/* end of decrease gap */
/* center header */
#header-inner img {
display:block;
margin-right:auto;
margin-left:auto;
}
/* end of center header */
/* decrease space under header */
.tabs-outer {
margin-bottom:-2px;
}
/* end of decrease space under header */
.sidebar .widget {margin: 5px 0;}
Change #px in a manner that will suits your needs