Improving GPU memory

So I just bought the Pavilion 15 cd051nr and the GPU  memory stated up to 4.32Gb  using  AMd a12 integrated APU.  When i checked the Radeon  R7 settings it says 512Mb.

 Is there a settings I have to change to enable all 4gb of gpu memory or do i have to install a seperate gpu card??? and if it is the latter how do i go about installing it???