themeszone

The plugin once activated will display a quantity field with increment / decrement buttons once add to cart button is pressed (e.g. the product is added to cart). 
Thus allowing customers to change the products number in the cart with out having to go to shopping cart 
page.
<a href="http://plugins.themes.zone" rel="nofollow ugc">PLUGIN DEMO</a> 
(click “Add to Cart button to see it in action”)
Feel free to ask any questions at <a href="https://themes.zone" rel="nofollow ugc">Themes Zone</a>

ThemesZone WooCommerce Ajax Quantity

ThemesZone WooCommerce Ajax Quantity Plugin shows quantity field on product listing once customer clicks "Add to Cart" button.

Nick Verwymeren

WooCommerce uses number inputs for the cart quantities by default, as most browsers now support <code><input type="number" /></code>.
However, you may want to have JavaScript powered inputs if you want greater control over appearance. Simply install and activate this plugin to do so.
It optionally includes a <a href="https://github.com/jonstipe/number-polyfill" rel="nofollow ugc">Number Polyfill</a>, which is a polyfill for implementing the HTML5 <code><input type="number"></code> element in browsers that do not currently support it.
To include this, add the following code to your theme’s <code>functions.php</code> file:
<pre><code>add_action( 'wp_enqueue_scripts', 'wcqi_enqueue_polyfill' );
function wcqi_enqueue_polyfill() {
 wp_enqueue_script( 'wcqi-number-polyfill' );
}
</code></pre>

WooCommerce Quantity Increment

WooCommerce Quantity Increment adds JavaScript powered quantity buttons to your cart page.

ThemesZone WooCommerce Ajax Quantity vs WooCommerce Quantity Increment