Yes,
BIOS is the only way to increase the vRAM to your Integrated Graphics.
If that BIOS setting is fixed or not showing then whatever amount of vRAM it has assigned is permanent. Many laptops has the option to increase or decrease the vRAM via BIOS Settings. But many don't. So it seems like you have a laptop that you can't increase the vRAM and is set permanently.
Besides, Windows will assign more memory when it is needed even though you only have the minimum amount of vRAM assigned. The Integrated Graphics may run a little bit more efficiently with more vRAM but you are stuck with what you have.
Unless ACER creates a new BIOS where you can change the vRAM. You can ask ACER Support if they have plans on a new BIOS with that option or not.