I was under the impression every time you fly to USA within a 2 year period you needed to update your ESTA so that your new accommodation details were updated.

I first got my ESTA last October when we flew to Las Vegas, we are going to NYC in March and I thought I needed to update my ESTA with my NYC hotel but I can't seem to find a way of doing this online? I don't want to get to NYC and have an ESTA showing a Vegas address if this will delay me getting through customs.

A card is required for Concur Gov and the Travel Management Center (TMC) to reserve a hotel for the Traveler.

To add a card, if one is not already there; select the “Add a Credit Card” link.

As others have said, customs is nothing to do with your ESTA.