AkhilM :
Well, it is a laptop so you won't really be able to upgrade anything. Honestly, the bandwidth difference is marginal, and devs wont ever optimize specifically for Skylake. If you really wan't to get the more expensive one, go for it! But for gaming, there will be no difference. (If you are willing to spend the money for the Skylake, I recommend to instead go with a better GPU ROG laptop, such as the 980m).
Some laptops do have an upgradable GPU, like the MSI GT60(I think), GT70, GT72, GT80. RAM, hard drive just about always. optical drive (if applicable) is likley, like going from DVD to a bluray writer. Sometimes you can upgrade the screen.
CPU, in the past, sometimes, skylake, not really.