It sounds like they've got the betatest package installed. The following should allow them to uninstall the package, and then install the DLS versions:
1) Double click on the Trainz icon on your desktop, then click on Trainz Settings.
2) Click on the 'Install' tab
3) Left click on the path shown in the 'LocalData Path' box, then press CTRL + A to select all, then press CTRL + C to copy it. The path will look something like 'C:/Users/%username%/AppData/Local/N3V Games/TRS22/build xxxxxxxx' if you have left this in the default location.
4) Shut down Trainz and ensure that tane.exe had ended (check in Task Manager no other or tane.exe processes are running)
5) Open Explorer (aka Windows Explorer, File Explorer, etc), then paste the path into the 'address' bar at the top of the screen.
6) Now open the folder called 'Packages'.
7) Please locate the file 2624.tzarc in the Packages folder, and then delete it.
5) Once you have deleted these folders, please then run a database repair.
To do this, first click on 'developer' on the launcher screen, then left click on 'rebuild database'. Once the repair has completed, the DLC pack will be uninstalled.
They should then be able to install the DLS version.