Dissolve the cleaner in 1 cup of warm water. Pour the solution into the water tank of your espresso maker. Alternatively, pour the lemon juice into the tank. Add additional filtered water until the tank is full.
Use a screwdriver to loosen the screw on the brew head (where the espresso comes out). Remove the screen from the brew head.
Place a coffee cup under the brew head. Place a coffee cup under the steamer wand of your machine.
Turn on the machine. Following your particular machine's directions, brew one cup of cleaner through the brew head and brew (not steam) another cup through the steam wand. Dump the brewed cleaner solution down the sink. Turn off the power and wait 30 minutes.
Run any remaining cleaner solution in the tank through the brew head and steamer wand (alternate between the two equally). Dump this brewed solution down the sink. Remove the machine's water tank and rinse it thoroughly. Put the tank back into the machine.
Fill the tank with filtered water. Brew the water through the brew head and steam wand (alternate between the two equally). Dump the brewed water down the sink. Repeat this with clean filtered water three or four times. Allow the machine to cool.
Replace the brew head screen. The smooth side faces downward.