Help i cant figure how to replace a terrain or texture

[steelknight999]

There is a really cool urban texture that I download yesterday but it said i need to replace it on something to use it on world editor but idk how plss help me.It said that i need to replace it on TerrainArt\Northrend\North_rock.blp but where the hell will i replace i plss help.

 

[Maker]

Import in in impot manager (F12) and change the full path.