RAM compatibility for AMD FX-8320

[a2w45mw3]

So i have an FX-8320 processor. I recently upgraded from an Athlon II to the FX. I currently had 16gb of ddr3 ram that runs at 1600mhz. My motherboard supports a max of 32gb, but when i upgraded to the FX, my pc is only using 11gb of my 16. Can some one tell me how to enable the last 5gb?

 

[CountMike]

That's your OS that's using that amount of RAM, how much does it show in BIOS ?