It is so simple just follow these steps:
1. Go to template
2. Edit HTML
3. Scroll down to CSS
Then copy and paste this into the space:
#header-inner img {margin: 0 auto !important;} #header-inner {text-align:center !important;}
This one works if you are using the designer templates if you
aren't using the designer template just copy and paste the first line.
Hope this helps you guys!
If you need more blog help this website is great!
http://www.bloggersentral.com/2010/07/template-designer-adding-custom-css.html
blessings,
Erin