This message was posted on behalf of Intel Corporation
I understand you would like to increase video memory in your computer.
Let me apologize for any inconvenience this issue may be causing to you.
The graphics controller that comes in the Intel® Celeron N2840 supports up to 1792 MB of video memory. You can confirm that on this link http://www.intel.com/content/www/us/en/support/graphics-drivers/000020962.html
Video memory setting can only be increased in the BIOS of the computer. Since there is no option in the BIOS to increase video memory then most likely the option was locked by the motherboard/computer manufacturer.