How I change the CPU

Hi,

Is the laptop overheating? Can you hear if the fan is working OK? Is the fan exhaust vent clear and unobstructed

The only reason you may need to refresh the thermal paste on a CPU, if that's what you're asking, is to eliminate the possibility of overheating due to dried out thermal paste, which reduces the effectiveness of the heat transfer by the fan and heat sink from the CPU.

Here's the maintenance and service guide for the laptop.

Go to p.66 to view the procedure to remove the heat sink assembly. This will allow you to remove the old dried out thermal paste from the CPU and to apply a new coating of thermal paste.

Here's the ifixit How to Apply Thermal Paste guide that may help.