I am sorry you are having problems to change the values for the dedicated video ram at the BIOS level but let me help you.
Note that the Intel® graphics controllers uses shared memory that is taken from the RAM memory installed on your computer.
The feature that sets the amount of memory that is used for video is called Intel® Dynamic Video Memory Technology and this will make the graphics controller only to use the amount of RAM memory that it requires to run the different applications or software’s.
I am afraid to say that there is no way to preset this to a specific value; however, you can limit the maximum memory that it can take only. You will see this option usually in BIOS and you will have 3 options, 128MB, 256MB and maximum DVMT. Other values can be found as 512MB, etc but this depends on the motherboard manufacturer and the amount of RAM memory installed on your computer.
I have setting in bios where i can change it but its grey.. What can i do to open that setting? I readed that on 4GB ram i should have 512MB but i would appreciate 256MB too.. cuz 128 is really low
Should i try to download that Intel® Dynamic Video Memory Technology ? Actually i never heard about that so i dont know if it is good idea
You may have the option to change this setting at the BIOS level depending on the Computer Manufacture. This can be enabled or disable by them only and I am afraid to say that we cannot pass the lock of the Computer Manufacture.
If you have the option locked, I recommend you contacting your Computer Manufacture for them to help you or confirming if that can be unlocked.