nVidia GTX 870M not detected

[m654321]

I have LL2.4 installed with Win8.1 in a UEFI enabled dual-boot set-up - working very well.

The laptop is an Asus G750JS, and comes with a dual GPU set-up: that is a default Intel GPU, and an NVidia GPU (Geforce GTX 870M), the latter kicking in when the graphics demand is high, e.g. when gaming. This system seems to work very well in Win8.1.

However, when I boot into LL2.4, the graphics are nothing special: the 'lspci' command in the terminal indeed reveals that only the Intel GPU is detected, not the NVidia one. 

My question is how can I:
(1) either silence the Intel GPU and use the NVidia one instead;
(2) or, better still, switch between either GPU whnever the need arises - I've seen online that some use software called bumblebee to do this but I have no experience in this deirection.

I've downloaded the lastest 64-bit linux driver (352.21) for the NVidia GPU from the NVidia website, but don't know how to install it properly.  I think I may have accidently deleted any existing NVidia drivers (331.67) that may have already been on the LL OS.

Any help much appreciated
Kind regards
Mike