When the wipers no longer clean well, the blades are probably worn or cracked.
To prevent damage to the wiper arms and other components, do not try to sweep the wiper arm by hand.
When raising both windshield wiper arms, raise the driver's side wiper arm first. When lowering the wiper arms, slowly lower the wiper arm from the passenger's side first while supporting it with your hand. Forcefully lowering the wiper arms could damage the wiper arm and blade, and may scratch or crack the windshield.
Raise the wiper arm.
Open the clip and slide the blade assembly in the direction of the arrow.
Tilt the blade assembly and remove it from the arm.
To prevent damage to the windshield let the wiper arm down easily, do not let it slap down on the windshield.
Pull down the blade rubber and slide it out of blade holder.
Remove the metal stiffeners from each blade rubber and install them in the new blade.
Do not bend or discard the stiffeners. You need to use them again.
If the metal stiffeners are switched, the blade's wiping efficiency could be reduced.
So do not use the driver's side metal stiffeners on the passenger's side, or vice versa.
Be sure to reinstall the metal stiffeners in the new blade rubber so that the curve is the same as it was in the old blade rubber.
Carefully insert the new blade rubber. Then install the blade assembly in the reverse order of removal.