Woocommerce quantity changing problem in cart page

Hi guys,
I am new to WordPress and since I created one e-commerce store using woocommerce plugin.
There is some page created by woocommerce plugin called cart, account, checkout, etc.
I already created store and its working fine when I place order for any product with some quantity suppose it is 5 each of $5 and I am going to cart page it is showing total ammount of $25.
but in cart page when I change the quantity of product the total amount is not changing.
So, please somebody help me how I can solve this, I want that instant change in total amount on quantity changing in cart page.