Add or remove memory in running a VM

On a Windows Server 2012 R2 or earlier Hyper-v server, you can't modify the size of the virtual machine that is running, and on the physical machine, you need to shut down the virtual machine to add or remove memory.

However, on Windows Server 2016 Hyper-v Server，you can increase or decrease the assigned memory at the virtual machine that is running.

Right-click on the virtual machine that you want to change memory, select setting，on the memory page，you can change memory in running a VM.

To change the memory allotment with PowerShell, you also can use the Set-VMMemory cmdlet