Get-VM -Name Infra2 | select *Memory*

Set-VM -Name Infra2 -DynamicMemory -MemoryStartupBytes 1GB -MemoryMinimumBytes 500MB -MemoryMaximumBytes 2GB

Créditos: http://techibee.com/powershell/increasedecrease-virtual-machine-memory-using-powershell/2084