Pretty easy. The instructions on how to change them are on the back of the packaging.
There is a small tab on the underside of the plastic cover (at the end of the arm) you need to push in and you can then remove the plastic bit holding the wiper blade. Then just tilt the wiper blade 90 degrees and it slides out of the pin holding it. Insert new blade and refit plastic cover.
Easy job, 5 minutes tops!