There are videos on the internet that can guide you on how to open your laptop and access the motherboard. Once there, you’ll need to unscrew the CPU heatsink, clean off the old thermal paste using isopropyl alcohol, and replace it with new thermal paste. Afterward, clean any dusty fans to improve airflow.
If you haven’t done this before on similar devices, I’d recommend consulting a local computer technician to handle the process. Older laptops can be challenging to disassemble, and there’s a risk of damaging cables or breaking plastic components during the process.