Go to the "Template" tab and hit the Customize button. From there, you can adjust virtually every parameter of the template you've previously installed. You can change the width of the main column and the sidebar, adjust background images and even move various blog elements (header, footer, sidebars) around.
The Advanced tab lets you customize the font, size and color of every last blog element, from links to headlines, post text, and everything in between. There's no need for your blog to look like a cookie-cutter copy of anyone else's. Don't be afraid to think outside the box!