How do you increase engine bhp?

Depends if its new or old. If the engine is run down, replace any parts that seem to be of poor maintenance, and check for any leaks or unwanted noises.

If the engine is new (or in good shape), you could add a turbocharger, supercharger, air intake, exhaust system, etc.

For more complicated engines, you can have a reflash of the ECU done, which can add anywhere from 10 to 75 bhp.