The installation text file with scenery says to delete all relevant scenery files before installing new OzRunways files.
What does "relevant" mean here ?
They want you to delete the default scenery so the new scenery won't load over it causeing a mess.
The chances are that it will ask you if you want to overwrite,..the answer is yes.
You probably won't be able to identify the default scenery, try that first.
:radar