Enter the following codes at the cheats option in the Settings.

Password	Effect
07401649	Master all levels in Medium.
22773762	Unlock Hard Mode.
23830252	Master all levels in Easy.
28077304	Master all levels in Hard.
58900895	Unlock Endless Siege.
67043273	Set stars to 5000.
77373872	No house damage in campaign.
82874356	Set stars to 20,000.
93456765	Unlock Specials.