Go to the Cheats menu. The right side asks you to enter the "Secret Codes". Click one and input the code. Make sure you activate it afterward if you want to use it.
GOLDENTRACKS - Tracks are solid gold.
BOTOFMYSTERY - Wall-E wears ski goggles.
EXPLOSIVEWORLD - All cubes are explosive cubes.
BOTOFWAR - Kills or stuns everything within range.
STEALTHARMOR - Can move undected by any enemy.
RAINBOWLASER - Laser switches colors continuously.
GLOWINTHEDARK - Lights up dark areas.