Get a high score in one of the challenge games, then enter any of the following codes as your name. Activate the cheats in the options/codes menu.

Password - Effect

1BH - Big Heads
5CM - Crazy Mode
3ES - Equalize Stats
4IS - Infinite Special
2TD - Time of Day
9AC - Unlock all cheats
7UK - Unlock Kits
6UP - Unlock Players
8US - Unlock Stadiums