jamon10, the only way to "unlock" the premium content is by purchasing it off of armorgames. If you click on the premium content button on the level select in the game it will give you an option to buy it, after which you can do so. If you're playing the iPhone, iPod touch, or iPad versions, however, you cannot access certain features (such as the extra reinforcement, extra starting gold and reinforcement costumes) while other premium content features come with the game.
