I just changed my wiper blades and as it was my first time, The £2 wilko wiper blades took me over an hour and I still had no luck, until I did some Youtubing!
1 Lift your wiper arm and make sure the wiper is perpendicular to the arm.
2 Remove the wiper from the arm carefully and then very very slowly let the arm rest on the windscreen
3 If you need to remove the adapter from your old wiper, follow the video and use two thumbs behind the adapter to push it out
https://youtu.be/T8i80mqesFE
4 Push in the adapter onto the new wiper blade
5 Reattach the wiper blade to the arm and voila!