Brake pedal goes to the floor

I changed my brake pads tonight and when I depressed the cylinder to allow the new pads to fit over the rotor I forced brake fluid from the reservoir. I have anti-lock brakes and think that when I forced that fluid out I messed the system up because now I can push the pedal to the floor every time I use the brakes. I have braking ability but it's not what I know it should be. Can you tell me how to reset the anti-lock brake system?