$spec = New-Object VMware.Vim.VirtualMachineConfigSpec
$spec.memoryReservationLockedToMax = $false
$spec.memoryAllocation = New-Object VMware.Vim.ResourceAllocationInfo
$spec.memoryAllocation.Reservation = 0
Get-VM | Get-View -Property Config.MemoryAllocation | %{$_.ReconfigVM_Task($spec)}