If you want to make different layout of Checkout page. Like this one:

Please just add to Theme Options -> Custom Code -> Custom CSS this code:

@media (min-width: 768px){
    #customer_details{
        width: 60%;
        float: left;
    }
    #order_review_heading{
        width: 30%;
        float: left;
    }
    #order_review{
        width: 40%;
        float: left;
        padding-right: 50px;
    }
    .woocommerce table.shop_table td{
        width: 50%;
    }
    .woocommerce .col2-set .col-1, .woocommerce-page .col2-set .col-1,
    .woocommerce .col2-set .col-2, .woocommerce-page .col2-set .col-2{
        width: 100%;
    }
}