In Main-Menu go to "Extras" then to "Codes" and you can type in the passwords. If correct it will confirm at the bottom of the screen.
GM2OPEN8 All Gamemodes
A11T3AM5 All Teams
MAXSKILL Max. Skills
Z26BEXW8 Micro Soccer
E06J3CT5 New Object in Inventory
SPEEDY01 Unlimited Turbo
5Y104D9A Unlock Streetballerteam
WIMP_A.1 Weak Opponents
Only tested on Pal-Version. Should work on NTSC too though.