Type your question here.how to fix CPU is underpowered..

You cant fix that message, its just an information message. You would have to physically upgrade the CPU inside your PC. 

If your computer is running fast enough for you, simply do not worry about it.  I did so for years.  It simply means that under load of today's average software, your computing experience would run faster and more efficientl if you replaced the computer to a newer one with a faster more modern CPU.