Choosing a New Design (Theme)
Browse, preview, and choose a new design template for your blog. This can be done at any time without changing or losing the existing content on the blog.
Click the Design Tab
Scroll through the themes, and click the image to see how one would look
If you want to keep it, click "Activate ...."
To cancel out of the current theme option, click the "X" in the upper right corner
Use the navigation page numbers or "Next" to explore more themes
When you find one to your liking, click Activate
You will recieve a confirmation message with your theme and a link to visit the site.
You can also visit the site as usual next to your blog title
You can see under the Design tab that this Theme has a "Custom Image Header" option
All themes have the same widgets, but some themes have more options. This one, and many others, have a custom header image option. See the tutorial on adding and uploading a custom header image to change the image in your header (not all blogs have this option).