Is there an easier way of deleting large amounts of terrain?

My game takes a very long time to load and I believe it’s because of how much terrain is in my game. I used the terrain generator and customized my terrain but the generator made the terrain’s height very large and and I need delete the bottom half off but I wanted to know if there was an easier way of deleting terrain without having to select it and delete it in small chunks…

Just looked in studio and there is a replace tool which grabs larger amounts of terrain.