my dell laptop specifications are :
Processor : intel core i7-4510U 2.00Ghz ( 4 CPUs)
Ram : 8GB
VGA : Nvidia GeForce 840M ( 2GB DDR3 )
and i plan to upgrade the VGA to 4GB Nvidia and the Ram to 16GB but i don't know if the cpu will work well with games with good fps and i don't know if this upgrade may reduce cpu life or it is safe ??
Assuming you are given the option of 2GB or 4GB for the 840m since you cannot increase the amount of VRAM yourself... the 840m is too slow to take advantage of more than 2GB. The only time I recommend 4GB for it is if you are working with large photos in photoshop and similar programs.
For gaming purposes you do not gain any benefits by having more than 8GB of RAM. Be aware that not all laptop will support more than 8GB of RAM. You need to check the specs of the laptop to confirm it will support more than 8GB of RAM, otherwise you are simply wasting time and money.