===>How to change cliff terrains?

===>How to change cliff terrains?

I started to create a map at the Ashenvale Terrain, but now, at a new version, i want to change the terrains to become like Northrend, but, how to change the terrains of the mountains (cliffs)!?
At the worldeditor is saying that terrains marked with red color cannot be added or removed, but, if anyone know a way to do it, tell me plx!

You need to change the tileset completely not just edit it. uncheck the "allow custom tileset" or what its called and then change tileset to Northrend.

Oh, Thnx!