Most major advantages are unlocked through the menu using "Exchange Points" earned from completing chapters with high ranks or playing the Mercenaries mode.
: Complete the main game once on any difficulty. Cheat Codes For Resident Evil 5 For Ps3
To use infinite ammo, you must first complete the main story. Once the story is finished, you must fully upgrade all attributes of a specific weapon to make its infinite ammo version available for purchase with Exchange Points in the menu. Most major advantages are unlocked through the menu