Not much, but this is a varying question, which means there are a lot of variables. Basically, it depends on if the business is an ecommerce store or brick and mortar store. Brick and mortar businesses, usually, keep the same design for a while , but ecommerce stores do the opposite.
You could look at getting access to many Website Templates and you can change your look pretty easily with templates. It's cheaper than hiring a web designer to overhaul it from scratch.