Replacing the hot end is a relatively simple operation. However, there needs to be some care taken when undertaking this repair. The Acrylic housing around the hot end can be broken if too much force is applied.
First Remove all leads from the hot end
The hot end should be disconnected from the quick connects which provide the heat core power.
Second, unscrew the bolts underneath the wooden slats
This may be slightly more difficult than it looks. The design of the extruder allows some free movement between the hot end and the extruder housing. Because of this, it may be difficult to work the screws free.
If you have trouble with this, I suggest that you wedge a small object, perhaps a pair of tweezers between the wooden slat, and the extruder housing. This will give you some leverage to get the bolts off.
Next, pull the hot end forward out of the extruder housing
This is simple, but you must be very careful while doing this, so that you do not crack your acrylic parts. Some units are a tighter fit than others, and so your results may vary. If you feel that the hot end does not want to come forth, do not force it. Instead, turn the hot end a bit trying to loosen it from it's position.
Finally, replace the hot end
Push a new hot end into place, exactly where the new hot end is. Screw the bolts back, and replace the quick connects.
*video of entire procedure*