You will need to check in your Laptop's BIOS setting to see if there is a setting for increasing or decreasing the IGPU vRAM memory.
8Generally the minimum amount is 528 MB up to 2 GB of System Ram can be used for your IGPU. But in newer laptops the maximum is probably higher than 2 GB.
If there isn't any BIOS Setting to decrease the vRAM for your IGPU then Lenovo has made the 2 GB RAM memory permanent.
Also in a laptop you might not be able to disable the IGPU since it works together with the discrete GPU card.
Best thing to do is increase your Laptop's System RAM Memory to 16GB if possible.