dust

My laptop runs very slow, it also makes sound so I'm pretty sure this means it's dirty. I unscrewed everything, unplugged battery but can't still open it. How do I open it to access the fan? Also I don't have a compressed air can, can I just clean it with only a toothbrush? Or a paintbrush?

hello guys laptop started to make clicking sound once in a while, i cant hear it when i listen to music only very silent click, nor when gaming. it is completely random Dell laptop , one click. could it be the fan from the dust? cani clean it without taking the back off?

So i have this complicated laptop http://www.sony.co.in/product/svs13a15gg . I cannot find fan , and i want to know how to clean it ?