The most common and easiest way is to clean the dust from your graphics card.
While some people swear by a benzene-free cleaning solution specifically designed for cooling devices, I just use water with a microfiber cloth that doesn’t leave lint behind. Spray the rag with the water and then wring it out so you don’t apply too much moisture at once, since overly wet surfaces can damage components in your computer.
Run the cloth over your graphics card’s metal exterior from top to bottom in one direction– this ensures an even coat of moisture on all surfaces without leaving streak marks–then run dry-side down on top of it in another route until most of the water has evaporated without immersing or submerging the card.
A fan on your graphics card may also be faulty, or could simply need to be cleaned, which can sometimes require its removal for access. If the fan itself isn’t turning, it may be gummed up with grime or hair, which can slow it down and cause it to overheat. Even if it’s spinning, however, the blades inside might be damaged, again preventing proper cooling.