You can change the detail level of the terrain with the Terrain Quality feature.
Location of Terrain Quality Feature
You can access the terrain quality feature from the Terrain Settings dialog, General tab, Terrain section.
Enter the settings of the terrain you will change the quality.
Move the pointer from lower to higher from the Terrain Quality section.
As you pull the pointer, the terrain detailing in the preview will change.
Click the OK button to close the dialog.
The terrain detailing will change.
You can bring the pointer to a level that will give the most optimum performance according to the hardware power of your computer.
Lower terrain quality
Higher terrain quality