During play, press the ~ key to bring up the console. Now type remoteadmin

1 and press Enter. Then, type in LOGIN developer and press Enter to

enable cheats. Enter the following cheats in the console and press Enter to activate.

NOCLIP (0 or 1)       Turn clipping on/off  
GOD (0 or 1)          Invincibility 
FLY (0 or 1)          Flying
UAMMO (0 or 1)        Unlimited ammo
GIVE_ALL              All weapons & Ammo 
ENABLE COUNTER        Show framerate 
ENABLE CROSSHAIR      Show crosshair 
ROTATE CROSSHAIR      Different crosshair

LOADSCENARIO("UMC_SPSCENARIO1","Level")    Level Select. Choose from the list below:

bootcamp
cube
vertigo
brooklynsp
illegal
station
warehousesp
tucson
border
mansion
house
haunted
temple
gothic
space
plant
deadend 

NOTE: You must complete Bootcamp before the level select codes will work.

Thanks to Revolution readers joakim and Jordon Reynalds!