Turn off the water supply to the sprinkler system.
Open and remove the lid to the valve box. Use your hands or a small garden tool to remove any mud or debris that has built up from the excess water leaking.
Shove some rags or towels into the bottom of the valve box. Allow several minutes for the towels to absorb the excess water around the sprinkler.
Unscrew the solenoid valve located on top of the sprinkler. Allow the water to drain from it.
Remove the screws that hold the top of the sprinkler, or bonnet, to the bottom portion of the sprinkler. Hold the top of the sprinkler down with your free hand as you undo the last screw. The top will fly off because of the spring underneath if you don't hold it down.
Lift up the top of the sprinkler from the bottom portion. Once you have raised the top a few inches, you can grab the spring underneath so it does not fly away into the yard.
Remove the rubber gasket on which the spring was resting. The gasket is typically responsible for most sprinkler head leaks. Replace the rubber gasket with a new one.
Set the spring back on top of the new gasket. Hold the spring in place while you place the top of the sprinkler back on top of it. Push the sprinkler head down and quickly let go of the spring with your other hand.
Screw the sprinkler head back in place with the screws you removed earlier.
Screw the solenoid valve back on top of the sprinkler.
Remove the towels from around the sprinkler. Turn the water back on.