How do I go about replacing the left crank arm on my bicycle?

To replace the left crank arm on your bicycle, you will need a crank puller tool, a wrench, and possibly a new crank arm. First, remove the pedal from the crank arm. Then, use the crank puller tool to remove the crank arm from the bottom bracket. Finally, install the new crank arm by screwing it onto the bottom bracket and tightening it with a wrench. Make sure it is securely attached before riding your bike.