To know what a guest is using you need to interrogate the guest directly. It then becomes a matter of the tools and methods you use to ensure you're looking at the right data. It's very common that vendors ship their appliances with such reservations in place so they can effectively say, "our stuff is more important than your stuff". If you know it isn't using it, the reservations aren't necessary. At the same time, if your motivation to remove those reservations is to free up resources for use elsewhere, it's likely you have resource exhaustion to begin with and need to address your problem at your infrastructure layer.
Also, why post this in ESX 4? Please move to vSphere or another more visible sub-forum (unless you're actually doing this on ESX 4 and then may God rest your soul).
Thank you for your response. So if understood correctly, if the guest OS is not over-utilized then there is no need for system reservation? I understand that the system resources are allocated but is there a way to know how much resources are allocated exactly over a period of time to the guest OS when the resources aren't reserved.
I searched for ESX 5 or 6 forum but I could find only ESX4, hence, tagged it in there.