How do I load the next level after destroying an object?

What to tell the script if i destroyed 10 turrets then he loads next level (if you understand what i mean)

I need to know this. What scripts do you need or just write code example

(short version)
My first level has 3 turrets but when i destroy them i dont move on to the next level

http://unity3d.com/support/documentation/ScriptReference/Application.LoadLevel.html