Turn on your fire strobe box and attach it to your camera as you normally would. It is usually mounted above your equipment.
Look at the side of the fire strobe box and find a small dial. The dial has numbers on it, typically from 1 to 10, although different makes and models could have different numerical settings. This is the number of strobes the box will produce per second when you turn it on.
Slide the dial higher. If it is set at 10 already, or if it is at the highest setting, you cannot make it faster and need to buy a different strobe. If it isn't set at the highest setting, turn it up and experiment.