The answer to 'how to install switch' is to first turn off the power to the circuit at the circuit breaker or fuse box. Then, remove the existing switch and disconnect the wires. Mount the new switch in the electrical box, connect the wires according to the manufacturer's instructions, and secure the switch in place. Finally, turn the power back on and test the switch to ensure it's working properly.
It's important to take safety precautions when working with electricity, such as using insulated tools, wearing rubber-soled shoes, and ensuring the power is turned off before starting the project. If you're not comfortable working with electricity or the installation seems complex, it's best to hire a licensed electrician to do the work.