Change cart input box to dropdown box

I am trying to do some minor customisation of my new site.
I am trying to do some minor changes to the layout of the cart box.

How do i go about changing the input box to dropdown box?
Can i elongate the box to cover the whole part instead of the left side?

Php 4.4
Zen Cart 1.3.9h
New install

What kind of "input" box? Text? That is a completely different kind of option. You can make new option names to replace the old ones, or possibly edit the option name to dropdown type. We really need to see your site to advise correctly.

I am trying to modify the cart

1. input box from current input type to dropdown type.
   (similar to x-cart)
2. the whole cart box from side to cover the whole middle section.

The "units in stock" is part of the product details, which you can set to display or not in Catalog > Product Types > Product-General > edit layout.

You would edit the add to cart box layout in /includes/templates/your_template/tempates/tpl+product_info_display.php. The add qty input type may be editable in that file as well, but I wouldn't know the details of how to change a form input type.