Edit order form headings

You can change any text in HikaShop by overriding is translation as explained there:
www.hikashop.com/en/download/languages.html#modify

For the quantity box, it's because you edited your front end CSS before updating so you didn't get the new CSS below that we added to fix that. You can add it yourself:

.hikashop_cart_product_quantity_delete, .hikashop_cart_product_quantity_refresh, .hikashop_product_quantity_field{
float:left;
}