Why are my games still lagging on my 4gb RAM Lenovo G50-30?

Ive tried playing skyrim, just cause 2, dead space 3 and some other games which require 2gb ram to play but they are still laggy as hell and unplayable. I dont understand how it says thats the minimum requirement is 2gb ram to play yet it still lags, especially skyrim. The lenovo has an intel graphics driver and 4gb ram, so surely this would be enough. Even fallout new vegas, which runs fine, lags major in areas with alot of lighting. If i was to upgrade it to 8gb ram, would this solve the lagg? As 8gb is the most i can upgrade it to.

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