This question has been posted many thousands of times on the internet. A simple Google search would probably list many links.
However if you want to learn something and retain it try the following...
Take it completely apart and study it and determine how it functions. Then put it back together and see if it still works... then try adjusting it to where it will be crisp, safe and not lighter than 2.5 pounds. If that does not work, take it to some one qualified.