When the wipers no longer clean well, the blades are probably worn or cracked. Replace them.
CAUTION
To prevent damage to the wiper arms and other components, do not try to sweep the wiper arm by hand.
NOTE
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.
1. Raise the wiper arm.
2. Open the clip and slide the blade assembly in the direction of the arrow.

3. Tilt the blade assembly and remove it from the arm.

CAUTION
To prevent damage to the windshield let the wiper arm down easily, do not let it slap down on the windshield.
4. Pull down the blade rubber and slide it out of blade holder.

5. Remove the metal stiffeners from each blade rubber and install them in the new blade.

CAUTION
So do not use the driver's side metal stiffeners on the passenger's side, or vice versa.
6. Carefully insert the new blade rubber. Then install the blade assembly in the reverse order of removal.

Wiper Blades
BatteryMazda 6 Owners Manual: Front buckle removal/installation
1. Perform the following procedure for vehicles with seat belt warning.
(1) Disconnect the negative battery cable.
(2) Remove the front seat.
(3) Disconnect the buckle switch connector.
2. Perform the following procedure for vehicles without seat belt warning.
(1) Remove the console.
...
Mazda 6 Owners Manual: Underbody Maintenance
Road chemicals and salt used for ice and snow removal and solvents used for dust
control may collect on the underbody. If not removed, they will speed up rusting
and deterioration of such underbody parts as fuel lines, frame, floor pan, and exhaust
system, even though these parts may be coated ...