Can't give any information as no upholstery cleaned yet...only floors and tiles.
MfG HJ

In general, steam cleaners cannot be used to thoroughly clean upholstery, but only to freshen it up a little. For a real cleaning, there are special upholstery or carpet wet cleaners. These loosen the dirt with water and detergents and suck the dirt out of the fibres. There are a wide variety of such devices, among others from Kärcher.