How to restart story in Need for Speed: Unbound ?

The answer can change depending on the platform you're playing Unbound on. If you are on PC, go to (Documents > Need for Speed Unbound > SaveGame) delete it and you should be able to replay the story. However you should take note that any progress you've made such as cars, driving effects etc. will be gone. 

it works, thank you

I wish the game had an in-game way of restarting as well having support for multiple saves.

What about limited edition items will they disappear too?