When I did mine, I removed the cover (which was easily the most awkward part because I couldn't work out how it was supposed to come off!) then lifted the arm so it was perpendicular to the windscreen. When it was like that, it was easy to wiggle it until it came off the spindle. When you see the arm come off, look at the angle the blade is compared to the joint/ring which sits on the spindle. You can see the angle of the arm to the spindle - the blade exerts a fair amount of pressure when it is flat against the windscreen, so no wonder some people struggle to get it off.