How can you improve a CPU's performance?

There are a number of ways. I would start with the fundamentals. Implement a scandisk and defrag. Then move to software which will remove spy and malware, there are many to choose from. I favor MalwareByes. You may google that to find the URL.

Finally, I would research what kind of computer I was using in conjunction with the task(s) I was requesting. Modern day tasks are not very easily accomplished on an elder pc.

One final thought would be to use the "task manager" to see what active programs are requiring the most usage for RAM and CPU. This can be accessed by pressing Ctrl+Alt+Delete at the same time. You may view the processes tab there. It will display what events are requiring what resources. The higher the number. the higher the resources. If you are unsure whether or not it is a required event, google it!