Changed the title. What specific Dell laptop model? Some models cannot upgrade the GPU. Does CS mean Counter Strike? Go here, look for the specific game, click "Can You Run It".

Hello Chris, It is Dell Inspiron 5559 model.

I will be worrying about system performance while playing high end games with Intel HD 520 mb graphics card.

Is this model good one if we are playing any such games like  counter strike .

Will there be any system performance degraded  as main memory (8 GB RAM) is shared across GPU ??

You need to run the application I linked to earlier to see how it will perform in that game.