The radio drivers are pre-installed on the Nanostation. No need to install anything, they run out of the box.
Do you mean how to install drivers on your computer? Do a search for your very first forum post and you'll find the answer.
Do you mean how to UPGRADE the firmware for the NS? Its explained in the AirOS manual in the UBNT Support web page.
This may be of immense help to you. http://winhlp.com/node/89