VirutalBox - Increase the memory on an existing guest machine

I use VirtualBox to run a guest Windows XP machine on my Mac. When I set up the virtual guest I set it to use 512MB of memory. And of course now I decide I want to bump it to 1GB. I could not find anyway to do this using the GUI but it can be done from the Terminal.

When the virtual machine is not running execute this command

VBoxManage modifyvm XP1 --memory 1024

XP1 is the name of my guest machine, so replace with yours. The memory parameter takes the amount in MB, in this case 1GB

The first time I ran it I received the following error message

ERROR: The machine is not mutable (state is Saved)

Last time I turned off the guest machine I had selected the save state option. You need to Power the virtual machine down before you can run this command.