How do I change width of fields in cart?

Hi,

The width of the columns of the cart should be changeable by editing the CSS of HikaShop via the Display tab of the configuration.
By default, the columns of the cart do not display like in your screenshot, so it would appear that you already changed something on that end, or maybe it's the CSS of your template.

In any case, we would need to look directly at that page on your website with Firebug to tell you exactly what CSS to change/add. Could you provide a link ?

That comes from the CSS:

p {
margin: 0 auto 0px;
width: 790px;
font-family: Arial;
font-size: 9pt;
text-align: justify;
}