Learn about Windows PowerShell
Summary: Use Windows PowerShell to add processors to a virtual machine running on Hyper-V.
How can I easily add processors to my virtual machine?
Use the Set-VMProcessor cmdlet:
SET-VMProcessor -VMname "My Virtual Machine" -count 2
This enables the virtual machine called "My Virtual Machine" with two (2) CPUs (presuming the computer is already shut down and you have two processors to work with).