Since this is a 4yr. old laptop, you need to truly access your innards. Depending on your skill set and laptop model, makes it al the easier. However, do this with deft care. I suggest first visiting the laptop maker support website and see what is offered to access the inside of the PC and what it takes. Easier laptops allow quick access and removal of the exact correct screws or toggles to get inside. Next, you closely inspect and check the cooling area(s). A good can of air will do wonders even if done from the outside. A direct and even close blowing out the dust is better than outside. Also, you actually your work being done. You may need to remove "heat tube" cooling as they tend to jam or allow fine dust to collect too readily or clog the vents and fans reducing the overall cooling effect. Sometime blowing out duct may become clogged in the exhaust exits as well, here you can see of directly blow out directly. Also, at 4yr. very fine dust or coating is on the fan(s) and access from underneath with a decent brush is better than blowing off alone. All this is up you and your skill set but its easier than you think or at least check to see it involves or proceed for a tech to do this.
tada -----Willy 