Hi @eminb, You may shut down the virtual machine to be enabled the settings to change the virtual RAM. But please pay attention when exceeding the recommended RAM value - your overall Mac performance may be significantly decreased (even down to computer freeze).
The maximum amount of virtual RAM depends on the total amount of physical RAM directly: you cannot assign more RAM than your Mac has. So, assigning 6GB for Windows will slow down your entire Mac functions and we do not recommend you to do that.