Since you have 8GB, first you need to check if that is one or two memory modules. Most likely it is only a one module, so the memory is operating in single channel mode. To get to 16GB you can install another 8GB module in the memory slot with a securing clip that matches the color (white or black) of the module currently installed. By pairing your memory in this manner you memory will operate in dual channel mode. If you add two 8GB module to your current configuration you will have 24GB but your memory will operate in single channel mode.