Grasp the centre of the wiper arm and lift it up and away from the rear windscreen. You may feel some resistance halfway – this is the lock position. You need to pull the wiper arm past the lock position so that it doesn't fall back onto the windscreen.
Pull the lower part of the blade away from the wiper arm until it loosens.
Press the new blade into place until you hear a click.
Check that the blade is firmly attached to the wiper arm.
Fold the arm back down against the windscreen.
Connect the wiper blade's hose to the hose connector. Lower the plastic cover back down.
Note
Make sure that the hose is positioned in such a way that it won't become trapped or pinched when the plastic cover is lowered back down.