Changing your wiper blades is simple do-it-yourself job. Problems like streaking are normal after a period. Change the blades when they no longer wipe uniformly. Even if you live in a dry season/wet season area like California, and don't use the wipers much, the rubber in the blades can deteriorate in the heat and sun. Change the wiper blades at the beginning of the rainy season there--preferably before it rains, but if you're a procrastinator, then under some kind of canopy.
Check the wiper blade size. Problems can be encountered installing the blades if you don't have the correct wiper size for your vehicle type. The Rain-X website has a menu-driven wiper-size calculator (see below),
Park the blades in the middle of the windshield. Turn off the car when the blades' cycle is in the middle and they should stop there.
Lift the wiper blade off the window. If you have a J-hook type arm, just depress the button on the clip and pull the blade out of the open end of the J. If you have a pin-type arm, use a screwdriver to remove the blade from the clip.
Install the blade. There are four types: J-Hook, P&H, Pin and Bayonet arms. J Hook arms are the easiest because the pre-installed connector will fit. Align the J hook around the connector and tug until you hear a click. The package has different size connectors if your J hook is very large. To install a P&H arm, replace the pre-installed connector with the P&H connector. Align the wiper blade so it's perpendicular to the arm and rotate until it aligns with the blade. For pin arms, remove the pre-installed connector. Align the pin arm with the relevant frame hole and slide the frame onto the pin arm. Click the universal adaptor on. For bayonet arms replace the connector with the bayonet connector and insert until it clicks into place.
Run the wipers and check the window is being cleaned properly. If the window still isn't being cleaned adequately, even after replacing the blade, make sure that you haven't left the clear plastic wrapper on the blade.
Give everything a good tug, to make sure it's all secure so the blades don't come off inadvertently.