I own a HP 15-d009tu with 4th gen PQC & 2GB DDR3 RAM 1333MHZ but I wish to upgrade it to 6gb of RAM, when I contacted a near by repair shop he told even if I upgrade RAM to 6gb my system won't use more than 4 GB anyway and there is no requirement. So do tell me whether I should opt for 4gb or 6gb configuration (total RAM, Including the 2 GB)