Currently the only way to remove an item in my shopping cart is by clearing the cart entirely. There is no option to do so individually or to edit the quantities from the shopping cart.

I'm using simpleCart.js which I have at http://yogasports.biz/simpleCart.js
and the coding for my form on my item pages looks like

Code:
  
<input type="hidden" name="on1" value="Color">
<select name="os1" class="item_color">
    <option value="Black"> Black </option>
    <option value="Grey"> Grey </option>
    <option value="Lavender"> Lavender </option>
    <option value="Mint"> Mint </option>
    <option value="Pacific"> Pacific </option>
    <option value="Pink"> Pink </option>
    <option value="Sea Green"> Sea Green </option>
    <option value="Red"> Red </option>
    <option value="White"> White </option>
    <option value="Currant"> Currant </option>
    <option value="Navy"> Navy </option>
  </select>
  &nbsp;
<input value="1" class="item_Quantity" type="text" size="3">
<span class="item_thumb">http://yogasports.biz/products/thumbs/w1001.jpg</span>
<input type="hidden" value="W1001" name"on2" class="item_style">

 &nbsp;
 <span class="item_price">$54.00</span>
<br /><p id="link" align=left> <a href="javascript:;" onClick="MM_openBrWindow('/images/alosizingchart.gif','Size Chart','width=220,height=410')">Size Chart</a></p>

<br /><BR />
<a class="item_add" href="javascript:;"> <img src="/images/add.gif" border="0" style="padding-bottom:50px" /> </a>

what should I change to allow quantities to be modified on checkout?