Level select:
Triangle, Triangle, Circle, Square, Triangle, Cirlce, Triangle, Square at the options screen. AN extra option should appear at the bottom of the screen, Level Number, which will let you go through the various levels.

All spells:
Enter the code above, then during a game press Triangle to access all the spells.

Increase mana supply:
Enter the code above, then during a game, press Square to increase your mana supply.

Complete the current level:
Enter the code above, then during a game, press Circle to finish the level you are currently playing.