When the wipers no longer clean well, the blades are probably worn or cracked.
Replace them.
To prevent damage to the wiper arms and other components, do not try to sweep the wiper arm by hand.
When raising both windscreen 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 windscreen.
Raise the wiper arm and turn the blade assembly to expose the plastic locking clip.
Compress the clip and slide the assembly downward; then lift it off the arm.
To prevent damage to the windscreen let the wiper arm down easily, don't let it slap down on the windscreen.
Hold the end of the rubber and pull until the tabs are free of the metal support.
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 don't 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.
Install the blade so that the tabs are toward the bottom of the wiper arm.