I understand that you are looking for a way to increase the dedicated video memory.
Regarding this, I would like to start by saying that there is no way to preset this to a specific value, you can only limit the maximum memory that it can take.You will see this option usually in BIOS and you will have 3 options: 128 MB, 256 MB and maximum DVMT. You can find other values as 512 MB, but this depends on the motherboard manufacturer and the amount of RAM installed on your computer.
This means that in order to change this value, if possible, you need to contact Asus*, they will guide you and let you know how to change it.
Also, could you please provide me with the Intel ® HD Graphics you have? or perhaps the model of the processor.
I hope this helps.