For now Octopress ships with a single theme in the .themes directory. When you install the Octopress theme, HTML and Javascripts are copied into /source and Sass stylesheets are copied into /sass. You are free to make any changes you like, but I've set up a few patterns to make it easy to customize and keep your site up to date with the latest Octopress releases.

I've broken this up into two sections.

1. Customizing the Template - Learn how to change the HEAD, sidebar, header, navigation & footer
2. Changing Styles - Learn how to change the color scheme, layout, and override styles

Also see Updating Your Blog »