A couple of suggestions.
1) If you are using windows xp me or 2000 than use system restore to go back before you added the scenery. But beware If you have added any other files or software those could be lost as well.
2) Not knowing what you have done before now forgive me if i am repeating something you have allready tried.
In order to remove scenery start FS and go to the settings menu then go to add remove scenery menu the last scenery you added will be the first on the list unless you moved it down a level. Once you find your scenry just click on it then click delete or remove. than restart FS.
3) You can also remove the folder where you put the scenery at. It is a good idea to make a seperate folder in the addon scenery folder for each scenery you add using the name of the scenery for the folder name. It makes things a lot easier to find.
If all else fails the only option left is to uninstall and reinstall FS.
