I need to decalcify my delonghi 4500

Descaling is another word for decalcification - I would consult the user manual for your exact model, because these directions are actually for the EAM3400, so there might be minor variations:
When the appliance displays the message:
DESCALE
You should perform the descale cycle.
Proceed as follows:
• make sure the appliance is ready.
• press the button (the light over the button comes on) then press the button repeatedly until
the appliance displays:
DESCALE NO
• Press and the appliance displays the message:
DESCALE YES
• Press the button to start the descale program.
• Empty the tank and pour in the contents of one bottle (4.2 fl. oz.) of DURGOL descaler plus 34 oz. of
water. For subsequent descaling operations, descaling solution can be purchased from authorized technical
service centers.
Note: Make sure splashes of descaler do not fall onto surfaces sensitive to acid such as marble, limestone
and glaze.
• Place a plastic or glass container with a minimum capacity of 50 oz under the hot water spout (Fig. 3);
• Turn the steam knob half a turn counterclockwise (fig.3). The descaling solution will run out of the cappuccino
frother and start to fill the container underneath.
• The descale program automatically performs a series of run offs and pauses to remove lime scale deposits
from inside the coffee maker.
• After about 30 minutes, the appliance displays:
DESCALING COMPLETED TURN KNOB
• Turn the steam knob a half turn clockwise as far as it will go (fig. 4).
The appliance must now be rinsed through to eliminate residues of descaling solution from inside the appliance.
Proceed as follows:
• Remove the water tank, rinse and fill with clean water.
• Reposition the tank.
• Empty the collection container (under the cappuccino frother) full of liquid and then put it back under the
cappuccino frother.
• Turn the steam knob a half turn counterclockwise (fig. 3).
18
Hot water is run off from the cappuccino frother into the container below and the appliance displays:
RINSING
• When the water tank is empty, the appliance displays the message:
RINSING COMPLETED TURN KNOB
• Turn the steam knob clockwise as far as it will go (fig. 4) and refill the water tank with clean water.
• The descale program is now complete and the appliance is ready to make coffee again.
NOTE: if the descaling cycle is interrupted before completion, the appliance continues to display the descale
message and the program must be started again from the beginning.

I believe the delonghi systems have;
DECALCIFICATION SYSTEM. Automatic decalcification indicator lights lets you know when its time to clean the machine.
I am not sure of the model you have so go to;
http://www.retrevo.com/samples/Delonghi-Coffee-Maker-manuals.html
to download a manual.
When you finish cleaning, flush the system with baking soda solution to neutralize the taste of any cleaning agent.