To install those dark background topic icons, upload "icons_dark_hd.pak", "dark_hd_smile" folder and "dark_hd_misc" folder to the "/your_phpbb_installation/images/icons" folder. Then, go to the Posting tab in the administration panel, and click Topic Icons in the sidebar. Install the icons_dark_hd.pak file with the "Install icons package" link. You can then reorder and/or hide icons via that page.