All you need to do is create a Post Process volume, then select the volume, and scroll down through the properties and check the Unbound box which will mean that the volume will affect the entire level instead of just the area that the volume covers. Then you can go through the properties of the volume to change settings.
A note about lens flares though–in UDK you would place a lens flare actor where you want a lens flare, UE4 doesn’t have that, it’s now a post process that gets applied to things that are bright enough, just like things would in the real world.