Unscrew the 4 screws holding the CPU heatsink and disconnect the fan.

Clean the old thermal paste from both the cooler and the CPU.

It's also recommended to use compressed air to remove any dust in the laptop and the fan.

Use only enough thermal paste to cover a portion of the pad. Use a spreader if you have one.

Place the heatsink back into the unit carefully and tighten the screws in an "X" pattern to ensure even pressure. Don't forget to plug in the fan cable.