title: How to override existing quantity already in cart?
body: <p>Problem I am having here is that people go to a Product page, set a quantity on how much they want of that product and add to cart (which than takes them to the cart page).  Client wants the ability to go back to the shop/product page if they want to make further changes to that product (honestly this is strange, since they can do this on the cart page, but whatever).  But when people go to update the quantity on the product page, instead of updating the quantity, it adds to the existing quantity for that product.</p>
  
  <p>How to get it to update the existing quantity when the quantity has been submitted more than once on the product page?  Is there a woocommerce loop that I can take advantage of here?</p>