It works the same way as the A4, as in, it uses system ram. The integrated graphics don't HAVE dedicated ram.
The reason your A4 is only using 512MB of ram is because that's what it's set to - look for an option in the BIOS to change that.
That's what I thought when I got the thing. My dad works in IT and that was his suggestion but there was no option, and since its in the same operating system/computer that won't change.
So what you are saying is that since there is no option in my BIOS to change it that even if I were to upgrade I'd still be screwed cause there will still be no way to change it....