Train 4 comes in four editions: Lite, Standard, Plus and Professional. They differ in the supported features and you can easily upgrade later by purchasing a new license. There is no need to do a reinstall or to make changes to your definitions.
In general the Lite edition is for users who only want to drive manually with their locomotive and to use the switchboard to easily set turnouts and signal.
The Standard edition adds fully automatic driving with or without routes.
The Plus edition adds decoder programming and multiple interfaces.
The Professional edition contains everything including networking (use of multiple computers/phones/tablets at the same time with optionally different operating systems) and/or to make use of a second screen (to display another switchboard and/or overviews) and no restrictions on number of objects.