https://www.dropbox.com/s/jjw6q2f2ew7tiqk/UnityGlitch.wmv
On the horizon where the rendering happens the mountains a glitchy, but the mountains that already rendered are fine. And also how do i change the render distance.
You can increase your rendering distance by selecting your camera and incrasing Clipping Planes → Far value. Generally that will not solve your issue. Please note that increasing far plane will also decrease your depth accuracy and may result in other artifacts as z-fighting etc. The solution would be to keep the drawing distance the same and adding some kind of fog, so terrain in the distance would fade into the background.