So now ETH is forking? Geez...
Anyway, not that I'm a crypto expert but I do know my software Basically a fork means there is a divergence in the source code of the coins. The original code base (Ether) moves on as is but Byzantium moves in a completely different direction. They are the same up to one point and that's where it stops. So if the fork happens at "change 3":
Ether: change 1 ------> change 2 ------> change 3 ------> change 4 -----> change 5
Byzantium: \-----> change A -----> change B
Hope that makes sense. In theory, you should have an equal amount of both coins after the fork and supply and demand or whatever will determine the value. Most likely one will fall and the other will maintain its value.
That's my take on it anyway (the crypto part). The software part is literally the same as going to the github repo, clicking the fork button and doing your own thing from that point forward.