How can I straighten the wheels on an open trolley? One wheel set has one of the wheels out of alignment enough to cause the trolley wag back and forth.

I notice there are two sizes of replacement wheels sold by Bachmann (Large 31.0 mm #92421 and small 24.5 Mm #92422). Which ones do I use for BH freight and/or passenger cars? I recently purchased a used Emmett Kelly Circus Train and it has plastic wheels that I want to replace.