You should replace your wiper blades about every six months. You can also examine the wipers for cracks. Old windshield wipers become hard and cracked over time, especially in a hot, dry climate. If your wiper seems to have lost it's rubbery spring, it's probably time to replace it.
How to Change Your Wiper Blades:
1) Find out what size blade you need to buy to replace them ( You will need to know the make and model of your car).
2) Once you have purchased the new wiper blades, lift the wiper arm in the air.
3) Press the small plastic stopper to unhook your old wiper blades.
4) Remove the blades
5) Match old and new wipers to see if they are the same size.
6) Put blade over arm and push down and pull out on the blade.
7) Push down until it locks in.
8) Put the arm down on the blade and test to make sure they are not scraping the windshield.