Open console (Tilde "~" for QWERTY keyboards or key "%" for AZERTY keyboard).

enter : Kingsoft 1

to activate cheat Codes.

Then you can use :

God 1 = God mode (God 0 to go back in normal mode)
FullLife = refill Max Health
fly 1 = Fly mode (useful to pass through walls or others obstacles) 
fly 0 = normal mode again
Reborn = ???