Either look up your vehicles' model and year in the wiper blade catalogs or see the NAPA AUTO PARTS Store sales associate. You can also take in one of your old blades to match up in the store. Some vehicles use different length wiper blades on the drivers and passenger side. Open the package containing the new windshield wiper blade. The package should include up to three or four different styles of blade attachments that secure the new blade to the wiper arm.

The blade and arm should now be sticking out perpendicular to the window. Some wiper arms will only come up two or three inches from the windshield. If you raise the wiper arm and it only comes up a small amount, don't force it. There should be a locking tab at the base of the wiper that will lock it in the raised position.

There are several styles: hook-slot connector, pin-type arm, wide-straight end, narrow-straight end, side saddle, pin-type blade, narrow-dead locker, flat hook and rock to lock. The three most common are the hook-slot connector, straight-end connector and pin-type arm.

Hook-slot connector: Swing the blade perpendicular to the arm so that you can see the connector. You'll find some sort of tab at the connector that either needs to be lifted or pushed to release the lock that holds the blade pivot in the hook slot. Once the tab is released, a firm shove toward the base of the arm will slide the blade right out of the hook slot.

Pin-type arm: Raise the arm and take a close look at the type of locking tab that holds the blade onto the pin. You'll either have to push the tab up from underneath the blade or lift the tab from the top with a screwdriver. Once the tab unlocks the pin, pull the blade assembly with a sideways motion away from the arm. The new unit may simply lock onto the pin. Sometimes, the box will contain an adapter that locks into the blade opening and accepts pins in different sizes.

Straight-end connector: The straight-end connector can be tricky. Sometimes you need to lift a tab on top of the existing blade with a screwdriver to clear the locking nub on the arm. You may also need to cock the old blade a few degrees out-of-parallel with the arm to slide it off the arm's end.

There will usually be a small tab you can depress with a screwdriver that will allow you to pull the blade from the arm. Some attachments have a small metal bump and two tabs on either side; depress the tabs and pull hard to remove the blade. Some just snap onto the blade. Once the old blade is off, apply a little anti-seize compound to the arm.

Test by turning on the wipers. If the blades slip, turn off the wipers and seat the attachments more firmly.