WordPress users may install and switch between themes. Themes allow users to change the look and functionality of a WordPress website or installation without altering the information content or structure of the site. Themes may be installed using the WordPress “Appearance” administration tool or theme folders may be uploaded via FTP. The PHP, HTML & CSS code found in themes can be added or edited for providing advanced features. Thousands of WordPress themes exist, some free, and some premium (paid for) templates.