Note: There is a trigger display ( like Quote) if you Go Advanced / Add Reply. You can use the option 'Copy as text' in the WE to copy it here and make it look like triggers.
I am not sure about the Display function.
Next steps depend on your choice. You can either order the tower via trigger to upgrade it, but then you have to prevent manual upgrade by players.
Or, other opportunity, you can remove the tower and create the upgrade one. This one is more difficult if you use more than one upgrade, I think it is done with hashtables or index, but I am bad with triggers, so I don't know.
Note: I don't pay attention to leaks, so may check the corresponding thread after you chose a way.