You can adjust the voltage coming out of the generator by fiddling with it's excitation system, whatever that is (varies by manufacturer and model), or by using a modern AVR or automatic voltage regulator as an add on. The frequency is adjusted by changing the rotation speed of the generator via pulley change or by changing the speed of the engine.
You need to study a bit more about generator heads and such before tackling this, or find a local person who is knowledgeable and can help you.
Most 60Hz equipment such as motors, lighting, electronics will run on 50Hz if you don't care to change the speed of the engine or pulleys.