Step by step instructions to import the landscapes into your level:

1. Install the FREE package Terrain Tools

2. Open the Terrain Toolbox

3. In the Create New Terrain tab, change the default Total Terrain Width and Total Terrain Length to 4096 or 2048

4. In the Create New Terrain tab, check Import Heightmap checkbox after that select the heightmap texture from this pack which you want to use as landscape/terrain

5. Press Create, in a few second your terrain will be imported.