This Seeking Tech guide will explain how you can change the difficulty in Metaphor. You won’t be able to change this setting in combat, so may have to reload to an earlier save if you get stuck in a fight.
Outside of combat, you need to bring up the Pause menu. If you are still early in the campaign, then you need to select Settings and Change Difficulty.
If you are deeper in the campaign, then there is an extra step you need to take. From the pause menu, select System and the Settings. You can then select Change Difficulty.
Keep in mind that you won’t be able to change the difficulty if you switch over to Storyteller or Regicide. Furthermore, you can only unlock Regicide in the new game plus mode.