Clean off any dust that maybe clogging one of the vents. People generally recommend using a can of compress air, but this forces the dust into the laptop with the hopes of it coming out of the exhaust vent. I recommend using tweezers to pull off any dust clogging the intake vents before using compressed air.
If it is still under warranty, then he should get it serviced.
If it is not under warranty, then he should consider replacing the thermal paste because it may have gone bad and is no longer effectively conducting heat away from the CPU and GPU. This involves carefully taking apart the laptop and documenting each step (pictures would be good too) so that you can put it back together again.
If you or your friend have doubts about your abilities to take apart a laptop, then it is best to bring it to a laptop repair shop.