Hi,
As some other people have stated, my Beta 1 says that it is up to date, and Beta 2 does not show up in the store for me to update to. I tried manually installing the update files to no avail as well.
I am running macOS Sierra Beta 1 currently on a MacBook Pro, Retina 15-inch, Mid-2014.
If you have this problem, comment as well, and maybe we can figure this out.