As in thermal image, hotest chip is not CPU, but LAN chip! and also Wifi dongle!

Anyway, CPU is a thing worth for cooling.

With heatsink, Raspberry Pi will decrease CPU temperature about 5 dgC (from 45 dgC to 40 dgC)

This is a passive way without any power consumption. How to make it?

Step1. Prepare a aluminium heatsink

Step2. Prepare heat silicone (other name: thermal grease)

Step 3. Coating a little heat silicone to CPU and heat sink 

Step 4. Stick heat sink to CPU

Step 5. Using cable tie to fixed them all.