The Intel(R) graphics controllers do use 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(R) 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. There is no way to preset this to a specific value, you can only limit the maximum memory that it can take. 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.
So, adding more Ram to the system may help the computer on performance but the options in the BIOS are going to be enabled depending on the system manufacturer decision.