Do keep in mind that the lead locomotive still carries the train's orders. You will find that the game UI resists you if you try to use drag and drop to remove the lead engine from a train. Try this:
1. # Send your train to a depot2. # Purchase a new (second) engine. It will appear on its own line, as its own train (with a new number).3. # Drag this engine into the older train right behind the lead engineusing your mouse. You will find you cannot directly place it in front. The newly minted train number disappears as the new engine is now considered part of the older train.4. # Drag the existing (old) lead engine to a position further back in the train, so it is no longer the lead engine. Make sure an engine (your new engine) is the first unit (the game won't allow a wagon to lead a train).5. # If you want you can now drag this old engine out of the train entirely (or just sell it in place).
Now you have successfully retained the train's orders but with a new engine in front.
Alternatively, you can use the game's dedicated UI for [[Renovation and Upgrade]].
==Train Vehicles==