Remove the top bezel (the one with the power button) by prying off from the slot on the right side-it'll pop off right to left, slowly and carefully. Remove the keyboard screws (3) on top, pull off keyboard from the top, pull it up and away slightly. there will be a ribbon cable attaching it to the keyboard at the end toward you. You can leave it plugged in.
Then shoot some canned air into the fan, then back through the exterior vents.
Watch the dust bunnies fly! Wipe the back of the keyboard near the fan. Theres a dust buildup there too.