Hi,
Well, in most cases, there is not much to do. You just update and it should continue to work like before.
But if you had customizations, 3rd party plugins integrated with HikaShop, etc, they might require modifications. But we can't give you a list of most common cases since we don't know the most common cases and usually everyone customize different things for different purposes. So it's hard to give a one size fit all answer besides: try the update on a copy of the website, and see what's wrong.