The PC gets hot because the fan doesn’t work properly, and the fan doesn’t work properly because it gets too hot as a result of running slow because of fluff and dust – a vicious circle.
Turn it off and let it cool. Turn it over – you’ll see a number of vents (grills). Keeping it moving run the vacuum cleaner over the grills taking care not to generate too much sustained suction at any one point – it could do more harm than good.
One vent – the largest bottom left back corner – is the fan air intake. Vac it well and make sure the fan spins freely.
Vac out the side vents.
Gently run over the ports – USB, Ethernet, Telephone/modem, SD cards, etc. and vac them out.
Make sure nothing is rattling inside.
Plug in and restart:
The fan should be quiet, the heat ‘normal’, and all well. And when the CPU is cooler, it’s more efficient and when RAM is cooler it will last much, much longer.
And, if not – it’ll need a professional strip down and clean and maybe a new fan.