Change Hyper-V Server 2008 Administrator password

Hi! I have a machine with Microsoft Hyper-V Server 2008 running. I put the Administrator password when I installed the system, but now... How can I change it?

I access the Hyper-V machine through Remote Desktop, and I can't see any option to change the Administrator password in the auto launched menu, only a option to add local admin accounts. The machine is not in a Domain.

Can I do from command line?

I also tried to using mmc from my computer, and selecting "connect to other server", but it gives me a error like "winrm client cannot process the request"

Thanks