Your laptop could have built up a lot of dust or the thermal paste that helps transfer heat from the CPU / GPU to the heatsink could have deteriorated.
If it is still under warranty, then I would get it serviced. Normally I would recommend a can of compressed air to get rid of / loosen dust, but this is a laptop and that could damage something or for the dust deeper into the laptop.
If it is no longer under warranty, then you can attempt to take apart the laptop to check for dust and replace the thermal paste. You should take pictures as you disassemble the laptop so that you know how to put everything back together.