While playing, bring up the console by pressing  tilde then type any of the following
NOTE: There is a space after the opening parentheses and before the closing parentheses in each code.
Code / Result:
@Password "Panzerklein" Activate Cheat Mode
@God0,1 God Mode
@Win0 Win Battle
SetIGlobalVar "Cheat.Enable.Chapters", 1 - Level select