Terrain loading help?

When I look at my terrain (both ingame and in the scene view) my fps drops to about 3. I have a slow computer, so this is sort of expected. I was wondering if there is a way to make my terrain decrease in detail as I get further away. Right now, the terrain itself remains smooth and fully rendered from a large distance.

So I'm trying to make it more blocky the further away I am, so that I can run around on it and not experience framerate issues. Any help / suggestions?