Using a 2.5mm hex key, loosen and remove the single fastener next to the heatsink fan.
Using a 2.0mm hex key, loosen and remove the fastener above the blower fan and the one right below it on the blower fan.
Carefully remove the blower fan and duct away from the part, it will still be connected by the fan wiring harness.
Using the 2.5mm hex key, loosen and remove the four fasteners holding the hotend assembly in place.
Remove the assembly by wiggling and pulling. Loosening the idler compression screw can help. Turn clockwise to decompress the spring.
If there is still filament stuck in the hot end, you will need to wiggle the filament guide loose from it.
Reassemble the toolhead as shown observing the following:
Take care to not pinch any wires when installing the new heatsink assembly.
The red ground wire goes thought the heatsink fins and on the bottom left short fastener.
The fan must be up on the heatsink before the fan duct is installed so that the wires are routed correctly.
Both heater pins go with the latch facing outwards.
The heater and thermistor wire pairs are not polarized.
For more details, see the Assembly OHAI