If you want to bring a guest, just talk to the staff.

One thing though, I tried to enter the lounge when I was gold, but I was only classic when I bought the ticket. It didn't show up as gold automatically, neither in check-in nor at the lounge. At check-in I had to tell them, in order to get my lounge pass (PVG *A lounge) and at IST, I had to tell the staff that I am gold, even though my ticket didn't say. They just checked on their computer and let me in afterwards.