WordPress Training: Previewing and activating themes
When you’re checking out themes in the Appearance, Themes menu, click on either the title or the thumbnail image of any theme and you’ll be given a full screen preview of the content for that theme. This will show you not only how the theme looks, but actually how your live blog would look, wrapped in this design. If you like what you see, just click on Activate Theme and that’s it, you’ll automatically be switched to that design, right away. If you’re not sure, or would like to check some of the other options out first just click the X in the left corner and your blog will remain wearing its current theme.
Bear in mind that you can narrow down your theme options with both the tags beneath the themes, which will show you similar themes or, up here, with the Filter drop down menu, and the Filter button. So that’s theme activation – have fun trying out different looks for your blog.