Inspect the sprinkler for damage. If the nozzle is broken, cracked or crushed, the sprinkler head will need to be replaced.
Pull the sprinkler out of the ground by turning it counterclockwise until it pulls free. You may have to remove some dirt from around the base of the sprinkler to get it loose.
Place the new sprinkler head on the supply line pipe threads below. Turn the sprinkler clockwise to set it in place, and aim the new nozzle in the direction of where you want the water to go.