The answer to 'how to install a circuit breaker' is to first turn off the main power to the circuit you'll be working on. Then, locate the circuit breaker panel and identify the specific circuit you need to replace. Carefully remove the old breaker and install the new one, making sure it clicks firmly into place. Finally, turn the power back on and test the new circuit breaker to ensure it's working properly.
It's important to take safety precautions when working with electrical systems. Wear rubber-soled shoes, use insulated tools, and avoid touching any live wires or components. If you're not comfortable performing this task or have any concerns, it's best to hire a licensed electrician to handle the installation.