To change the game's difficulty, edit the defuser.ini file in the game's folder using Notepad or a text editor.  Look for the section that begins with [HGame.Harry].  Look for the following lines:

fDamageMultiplier_Easy=1.2
fDamageMultiplier_Medium=2.0
fDamageMultiplier_Hard=3.0
 

Change the values to 0.1 to take less damage and make the game easier.  Save the file and start the game to take effect.