unable to change number of Cores without disabling?

I'm suddenly getting REALLY SLOW performance (running CAD software) in Windows 8 running on new MacBook Pro.

I'm attempting to reduce number of cores from 8 down to 6, but the whole settings window is gray'd out, and it says that I can't make changes until I disable VMWare.

But how can I make changes to the settings if VMWare is disabled?

I have already paused the session.

Also, I'm not sure why all of a sudden this configuration is running slow, when it was running very fast before.

(Separate issue?).

Thanks,

Greg