Take the cooler of,remove the thermal paste,re-aplly new paste and put the cooler back.
For thermal paste go to the local shop if you have that.Remove the old paste with a old clean cloth or toilet paper by using medical alcochol.First whipe the exces away,after that clean with the medical alcohol.
You could first check if the cooler is loose at a corner and push it back again.Also check for dust in the cooler or under the fan of the cooler.When there clean the cooler.