Usually hold the [ fn ] key and the [ f2 ] together or just the [ f2 ] key depending on how your "Hotkeys" are setup. If you've had a fresh install of windows or the drivers aren't working properly you can do it manually by going into the bios like so:
Turn on your Asus Netbook. If your netbook is already on, click the "Start" button, click the arrow next to the "Shut Down" button and then click "Restart."
Wait for the Asus Netbook BIOS screen to appear, then press the "F2" key.
Press the "Right" arrow to scroll over to the "Advanced" tab.
Press the "Down" arrow until you reach the "Onboard Devices Configuration" option. Press the "Enter" key.
Press the "Down" arrow to "Onboard WLAN" then press the "Enter" key.
If the "Disabled" option is highlighted, press the "Up" arrow to highlight the "Enabled" option, then press the "Enter" key.
Press the "F10" key. Press the "Enter" key to save your changes and exit the BIOS. Note: If you are missing your hotkey drivers you can find them here under the ATK section (Use the latest version) http://support.asus.com/download.aspx?SLanguage=en&p=3&s=670&m=F555LA&os=&hashedid=n%2fa