You will need the machine to be off, cooled down and have the water line shut off.
1. Turn off the water line, turn the machine off and let it fully cool. This step is only necessary if replacing the expansion valve seat. Adjusting it requires the machine to remain on.
2. Remove the front panel of the machine by removing the 2 screws in the front and pulling it out from the bottom. It will be easier to remove if you take out the drip tray.
3. Adjust the expansion valve by turning it the way shown in the picture. Left will loosen it, right will tighten it. If you find your expansion valve to be leaking, it may just need to be tightened a half turn or so. You will know the expansion valve is adequately adjusted if it stops leaking during a backflushing cycle.
4. If you need to replace the expansion valve seat, fully loosen it all the way until it pops out. Replace the fitting at the end of the spring and tighten the expansion valve back in place until the expansion valve does not leak during a backflushing cycle.