Okay, use compressed air to blow out the fans and heatsinks. Note that depending on design, you may need to separate heatsink fans from heatsinks to be able to properly blow out all the dust.
If you feel comfortable doing it, you can replace the thermal paste that is in between the heatsink and CPU/GPU/APU. Thermal paste can dry out over time and lose it’s thermal conductivity. There are general tutorial videos on how to do this, and it’s not very hard. As for cleaning off the old thermal paste, you can use thermal paste remover, or 90% or better isopropyl alcohol. Of course, the latter might be more difficult to come by nowadays.
Anyway, doing that will help your computer to better cool itself, which will hopefully allow you to turn your graphics settings back up.