HowTo/Consists / Locomotives / Trains
From TrainzOnline
The list of Consists, Locomotives and Trains available on the Driver in the current session is showed on the left side of the screen, along with the driver and the current command they are executing. If it is not shown, LMC on the picture of the current driver on the left bottom corner to make the the menu appear. To minimize it, LMC on the current driver's picture again. On the top part of the menu there are top and down arrow, LMC on either to cycle over the available units.
To change the current unit, LMC twice on the picture of the desired one.