To change your theme, go to the Appearances tab on the sidebar and select Themes. From this page, you may customize your current theme or change it completely by choosing from your available themes.
Selecting Details under any of your available themes will give you information about this theme. Selecting Live Preview will bring you to a preview page of your site with this theme.
You may further customize the theme by using the options on the left. You can activate the theme right from the screen or you may activate it through the Manage Themes page as well.
You may also install new themes from the Install Themes tab. From this page you can use the feature filter to select the criteria you want for your theme and hitting Find Themes. You can also choose recently updated, newest and featured themes to browse through.
You have the same options for each theme as the Manage Themes page, except you must install the theme before you can activate it. If you wish to upload a theme manually, select Upload at the top of the page. Pressing Choose File will allow you to select the zip file of your theme. To install your theme press Install Now. You can then easily preview and customize your new theme and activate it for the world to see.