You can upgrade up to 32, at least in the one I got, there are 2 ram slots and only 1 in use by a 16gb module, so I just need to add a second 16gb module for a total of 32. I had a 4gb module laying around so I tested it and it worked, 20gb total, I ended up taking it out because the 4gb module was a lower performance and cheap one, but it did worked.
Hope this helps and sorry for my bad English.