It is a very difficult task. You grab the blade and pull straight away from the arm. It pops right out.
To align the blade, I suggest running them a few times to ensure that they are finding their home position. If they are indeed still not aligned, fold the arm out, and you will see a nut, I think 8MM. take off the nut, pull the arm, turn it where you want it and push it back over the splines. then replace the nut and fold the arm back in place.