Is this a Laptop or Desktop APU?
Look in BIOS for a setting that sets the amount of System RAM use for your Integrated Graphics. Generally the maximum is 2 GB of System RAM but with the newer APUs that might be higher.
The lowest setting generally is, I believe, around 512 MB used for the Integrated Graphics of your APU.
So you need to enter BIOS and check anything to do with RAM Memory or IGPU settings.
On some laptops you can't change this setting and the amount of vRAM is fixed. The only thing you can do, in that case, is increase your System RAM Memory if possible.
