The U section (metal hook end) of the wiper arm does not move. All the action happens with the blade. Some blades have a plastic tab that you must press and hold to release the blade from the hook while sliding it out of the open end of the U-channel at the same time.

The blade's pivoting connector simply slides out towards the bottom of the arm (towards the arm's drive pin) once it's freed from the U-hook. I usually swing the arm away from the glass and move the blade so the blade and arm form a T which flexes the blade such that there's more room to maneuver.

(Or buy a wiper blade that has a fitting for U hook wiper arms, and just read the directions that come with it...) I've had good results with a NAPA store, and he put the blades in as a courtesy in less time that it took me to unlock the car....

Just like a 240 flame trap, it's easy after you've done it once to get a feel for it