How to clean laptop fan?

[FrozenToothpaste]

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?

 

[nigelivey]

Use a Qtip (ear bud)

 

[Phillip Corcoran]

"I just clean it with only a toothbrush? Or a paintbrush?"

Definitely not! They will generate static which can damage internal components.
Use only a can of compressed air.

Even with all relevant screws removed, the underside panel won't simply lift off. It's held in place by hidden plastic lugs/clips around the edges. You have to carefully prise the panel upwards all around the edges to "pop" the clips.