There are many ways to increase a car's horsepower, including upgrading the air intake and exhaust systems, installing a performance chip, and adding a turbocharger or supercharger. Upgrading the engine's internals such as the camshafts, pistons, and rods can also increase horsepower. However, it's important to note that increasing horsepower can also put strain on the car's transmission and drivetrain, so it's important to ensure those components can handle the additional power.