To change the difficulty in Prince of Persia: The Lost Crown:
 
•  Open the pause menu and select "System".
•  Choose "Options" and then "Difficulty".
•  Locate the Difficulty Modes option.
•  Choose between "Rookie", “Fighter”, " Warrior", "Hero", "Immortal", and "Custom".
 
The changes will be applied the next time you respawn at a Wak Wak Tree or by saving the game and relaunching it.
 
When selecting the Custom difficulty option, you can adjust the following options:

Enemy Damage
Environmental Damage
Enemy Health 
Boss Health
Parry Difficulty
Dodge Window
Athra Depletion Rate
Athra Gain
Athra Loss Rate From Damage