By default, KDE uses the Dolphin file manager. To modify the appearance of Dolphin windows, open the program by clicking the Kickoff Application Launcher > Applications > System > File Manager icon for Dolphin. At the top of the Dolphin window, click Settings > Configure Dolphin. The tabs in the Dolphin Preferences window allow you to specify the folder that Dolphin displays when it starts, the size of the icons it displays, the font it uses to label icons, and many other options.