memory allocation problem

Hello all

I'm running linux on my parallel desktop 7 and I'm facing a memory allocation problem.
I have 8GB of RAM and I want to allocate 4GB for my guest OS.As I try to increase the memory in the configuration settings, I don't see any error messages but when I start running my guest OS, I see that the increase in memory hasn't been applied.It seems that the allocated memory is 2.8 GB at most and it doesn't change as I try to increase it any further.

Any help would be greatly appreciated