-- in class definition

[DllImport("KERNEL32.DLL", EntryPoint = "SetProcessWorkingSetSize", SetLastError = true, CallingConvention = CallingConvention.StdCall)]
internal static extern bool SetProcessWorkingSetSize(IntPtr pProcess, int dwMinimumWorkingSetSize, int dwMaximumWorkingSetSize);

[DllImport("KERNEL32.DLL", EntryPoint = "GetCurrentProcess", SetLastError = true, CallingConvention = CallingConvention.StdCall)]
internal static extern IntPtr GetCurrentProcess();

-- code to call when you want to reduce the memory

IntPtr pHandle = GetCurrentProcess();
SetProcessWorkingSetSize(pHandle, -1, -1);