Many laptops doesn't have the option to increase the vRAM through BIOS settings. So if you don't find a setting in BIOS to increase your Integrated Graphics vRAM that indicates that Acer wants the vRAM to be permanent.
Possibly in a future Acer BIOS update they may add that option but until they do you are stuck with whatever amount you have now.
Besides, Windows will automatically assign System Memory so that your Integrated Graphics will be able to run any app in your laptop.
Also with only 8GB of RAM, even if you could increase vRAM it might not be a good idea since it is taking away a portion of your 8GB System RAM Memory which might make your laptop sluggish.