You can reset your Dock to its original settings (default icons, size etc) with the help of following steps-

  1. Go to Launchpad, select Utilities and Click Terminal
    terminal.png

  2. type the following command
    rm ~/Library/Preferences/com.apple.doc.plist; killall Dock
    Screen Shot 2013-04-04 at 3.49.02 PM.png


Now you can see the Dock is rest to its original configuration.