Question

How does wind and water change the size of mountains

Answer 1

The wind and water work to erode the mountains.

Answer 2

When water comes quickly down a mountain, sometimes, it takes some of the rocks of the mountain down with it.  That's called erosion.  As time goes on, water will take more and more rocks down the mountain, so that will make the mountain smaller.  Wind can also blow rocks down the mountain, that can make caves, and different types of forms in the mountain, and make the mountain smaller.