If your requirements have changed since you first created a virtual machine then we allow you to upgrade / downgrade it as required.
Downgrading a virtual machine can only be carried out with the virtual machine in question being shutdown first. An upgrade will generally not require you to shutdown the virtual machine but this is entirely dependent on the operating system in use supporting hot CPU and hot memory upgrades (most do these days). This upgrade / downgrade guide will presume that should you wish to downgrade memory or CPU that you have shutdown your virtual machine first and, that you will start the virtual machine after completing the steps below. To see how to shutdown and boot up a virtual machine refer to the Start / Shutdown a virtual machine how to guide.