At the Main Menu, press C-Up + C-Down to display the Cheat screen. Now enter any of the following:

Bonus Teams: C-Up, C-Up, C-Down, C-Down, C-Up, C-Up, C-Down, C-Down.
Big Heads: C-Up, C-Up, C-Down.
Long Necks: C-Up, C-Up, C-Down, C-Up, C-Down.
Small Player: C-Up, C-Down.
All players are smaller: C-Up, C-Left, C-Down, C-Right.