Squeeze. nVidia video. How to change brightness with functional (Fn) keys?

[Mark Goldshtein <mark.goldshtein@gmail.com>]

Hello, list!

Lenovo Y450-3M laptop with:
01:00.0 VGA compatible controller: nVidia Corporation GT216 [GeForce
GT 240M] (rev a2)
	Subsystem: Lenovo Device 38fd
	Kernel driver in use: nvidia

Would you, please, to explain how to configure a system or edit
configuration files in order to bring laptop brightness funktional
keys (Fn+key) to thier normal work? It is impossible to adjust
brightness pressing Fn+UpArrow and Fn+DownArrow keys. The symbol of
brightness is displaying well, but no adjust actually happen.

Googling left me unsure about what I have to do to correct this issue.
There are mostly comments from Ubuntu users. I know Ubuntu is Debian
based but need to be understanding what I am doing with my system. If
you have a little time, please, help.

Thanks in advance!

-- 

Sincerely Yours'
Mark Goldshtein