Purchase refills to replace worn rubber part of wiper blades. You don't have to buy the entire blade. Most often you can just replace the wiper refill as we show here in this how to change wiper blades article.

It is recommended that you change your wiper blades every 6-12 months. Windshield wipers are made from rubber which is degradable, and becomes less effective over time. You should get into the habit of checking your wipers regularly and know what signs to look out for as they begin to wear out.

Your vehicle's manual should tell you what size wiper blades you need for each side and could even recommend a brand. Some vehicles have different size requirements for the driver and passenger sides, so read carefully before replacing the blades.