Most of the time the rivet head holding the roller in place needs to be ground off, the roller replaced and a new rivet installed and clinched over. There is a special rivet press available to do this that is expensive, and there is also a hand held set that can be purchased, although the set is not cheap either.

As an alternative, most roller pickup assemblies bolt in place on locomotives, and the complete assembly can be replaced as a unit. Older roller pickup assemblies on rolling stock are also riveted in place as part of the baseplate/coupler assembly. Most newer rolling stock have assemblies that just snap in place, so replacement is fairly easy.

Without knowing exactly what trains you have, and their catalog/road number, it is difficult to give a precise answer.

Always give the rolling stock/accessory number in your posts so that a more precise answer can be given first time around.

Larry