Today I decided to update firmware of my wifi shield, so started reading the official papers, but not all goes how was planned (not a surprise). First I needed to change update script because paths there were wrong. Instead of wifishield how is the original installation script has wifi-shield. Also one hint on Mac, in order to run the script you need to use sudo bash ArduinoWifiShield_upgrade.sh -a /Applications/Arduino.app/Contents/Resources/Java.
One useful article helping mac users, you can find here:How to update the official Arduino Wifi Shield
Wish you luck!