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Tell us the model and specs of you MBP. Some have one others have 2. If it's a unibody MBP, you remove the bottom lid, disconnect the fan(s) cable(s) and unscrew the fan(s). Older unibody Macs have philips 00 screws, newer ones have special screws, but theres a scre driver for that. One the fan is removed, I blow into te heatsink vents, and blow into the fans. If really dusty in the fans, a cotton swab wet with water is used to remove the remainig dust. Sometimes (don't do this) I carefully poor a little water through the heatsink vents while keeping the electronics covered up. This ensures ALL dust is gone.