We rebuild the page closest to the sale, then run it against your current one on live traffic until revenue per visitor says which one wins.
Usually the product or offer page, because that is where the money is decided. One page, rebuilt properly, not a list of opinions about your site.
Your visitors split between the new page and the current one, tracked to revenue per visitor and run until the result is clear enough to act on.
An ongoing programme after the first win. Each test builds on what the last one measured, so the page keeps moving in a known direction.
Anyone can redesign a page; the difference is whether it is measured afterwards on your own traffic.