Go to "SPECIALS" and then go to cheats and enter any of the following codes:

Freakout-GreenGoblinSuit
Serum-ScientistSuit
Realhero-PoliceSuit
Captainstacey-HelicopterPilotSuit
Knuckles-Thug1Suit
Stickyrice-Thug2Suit
ThugsRus-Thug3Suit
Hermanshultzs-ShockerSuit

Now you get to be one of the following people, but don't exit out of the cheats menu yet. Now after you put the cheat you wanted to put in enter "GOESTOYOURHEAD" to make whatever character's head and feet huge.