Mix 1/2 white vinegar and 1/2 water and pour into the iron - turn it on till it starts to steam - turn it off and leave it overnight - turn it on again till just warm & then pour out the water & vinegar. Rinse through with clean water a couple of times.
Tip - if you live in a hardwater area then use bottled water from the supermarket - prevents scale build up - Hope i helped :)