I presume you mean getting the pulley off the pump itself ?
It has been a while since I did one , on a M102 , which IIRC is similar to the M103 , which in turn is the same as the M104 apart from the head . On the 190E , I had to take the radiator out for good access to everything - the job would have been difficult if not impossible otherwise .
If memory serves , the pulley is affixed to the pump by 3x bolts of something like M6 or thereabouts ( 10mm socket or spanner required ) . When I did it , I took the precaution of loosening the bolts before I removed the drive belt - that way I was able to press on the belt to increase friction and lock the pump while I loosened the bolts . If one is stubborn , you could try holding one of the others with a spanner while you have a go at the stubborn one . With all bolts removed , the pulley should come off , perhaps needing a knock with a hammer to free it .
