How to hack iPod games?

I want to hack the coins in machine-gun jetpack, but I have no idea how.
How do I do this? Does anyone have any idea?
Answer #1
go to cydia and add a source such as xsellize or as i use insanelyi. Download a program called iap cracker. Then go to jetpack joyride and get all your coins
Answer #2
Does this work for infinity blade 2? Im stuck on connecting when I wanna buy gold