Is there any way to get better graphics in need for speed most wanted on low end devices like iphone 4 like using hex editor or any other thing?If yes,please help me out
Not likely, only a few developers seem to allow you to change graphics settings like that. (I think Team 17 allowed it for their first Worms game) Not that I know of for Need for Speed however, sorry.
Lol you will care once the framerate drops to 10FPS And no, there's no way to modify the IPA on iOS 6 without a jailbreak.