Want to configure WNDR3700 as wireless range extender with Bell Sag Modem plus router

I have a Bell Connection Hub upstairs, which is producing wifi signals from my whole house, except basement's computer room which is in the corner, its range is not that much. So I bough Netgear WNDR3700, in order to use as WIRELESS EXTENDER.
I want to put that WNDR3700 downstairs in my basement, & I want to connect it to the Bell device without wire i mean through wireless and it will produce wifi signals in my basement as well, so that My pc can run on that wifi.
Please I want to know how should I configure it..step by step???