How to change monster power in Diablo 3?

I read that you can change the monster power in this game but can't find any info on the ps4 version. This game is way too easy, to the point it's not even fun.. I'm playing on expert mid way through act 2 and I can 1 hit almost any normal enemy. I think it's stupid that they don't let you up the difficulty until you beat the majority of the game (I think act 4). Is there any way to make this game more challenging without just ignoring new armor and weapons? I would rather just not play if that is the case.