What to do here? Edit listing or create new one?

One of our products – a 400ml shampoo – is changing size as we are offering it in a smaller package instead.

What do we do on the Amazon side of things?

Is it possible to edit the listing and update the GTIN on gs1 uk (this is what Amazon support recommended) –

Or do we have to create a new GTIN, delete this listing, and create a new one?

We are also registered in Brand Registry, so don’t know if that would need to change too?

Thanks