Should be able to just slide the box top up and off and plug it in while it still sits in the box.....if they won't do that at the store, do it yourself at home before you totally unbox it.
This is a good practice when you buy any set at any time, or any place to check for shipping damage.
I've seen quite a few sets that are shattered (cant tell until you plug it in) from shipping. even if the box looks fine.
(especially from Amazon)