I assume you mean video memory.
That's shared with the System Memory and likely adjustable in the motheboard BIOS (see motherboard manual). It's probably a maximum of 512MB or 1024MB.
If you're trying to game then 1024MB might be best. If not gaming then 128MB is probably plenty.
http://www.pvladov.com/2013/10/increase-intel-hd-graphics-dedicated-video-memory.html
You can install the program "cpu-z" and look at the "graphics" section however I'm uncertain if that is accurate for an iGPU. Probably it is accurate. If it shows a number like 256MB, 512MB, 1024MB it's probably correct.