I think you will get notification in Epic Games Launcher, when update will be released. So there is no need to redownload anything before update button will appear.
I didn’t use level streaming in this project, because it’s also required additional maps(and I have limitations). I just answered how to make two levels.
You can set FirstPersonGameMode in world settings, so in each new map first person character will be default character. You also need to set projectiles via array to this character somewhere in new level, because by default character doesn’t have them.