Because each faucet manufacturer differs slightly in the design of their pull faucets, you must purchase the correct replacement part. Contact the manufacturer of your faucet either by phone or email. The company will help you order the hose that best fits your faucet and send you specific directions for the repair. If you can't find the manufacturer information for your faucet, take a photo of the faucet to a plumbing supply store for advice.
The plastic of your sprayer hose will break down over time. To replace it, turn off your water supply and use a wrench to disconnect the hose from the water lines. Mark the position of the weight on the hose with a permanent marker. Use a screwdriver to loosen the screws on the weight and then remove the weight. Pull the hose out from the spout.
Each manufacturer will have more specific instructions on how to install your new hose, but the following will provide a general guideline to the process. Lay the old hose next to the new one and mark where to position the weight on the new hose with a permanent marker. If the new hose didn't come with a new nozzle, put the old nozzle on the new hose. Feed the hose into the spout. slide the weight on to where you indicated and use a screwdriver to tighten the screws to hold the weight in place. Reattach the hose to the water lines. Slowly turn turn on the water supply, checking for leaks as you do so.
If the spray on your pull out faucet feels less powerful than it used to, the screen between your nozzle and hose may be clogged. Turn off your water supply to the sink and then unscrew the nozzle from the hose. Inside the base of the nozzle you'll find a metal screen. Remove the screen and scrub it clean with a toothbrush dipped in vinegar. Replace the screen and reattach the nozzle before turning your water supply back on.