Paid app to free app distribution

I had a paid app on app store (e.g Old 1.1) and i am going to upload one more app (e.g New 2.0)开发者_如何转开发 not a upgrade and i want this app to be given to my old customers as free who had paid for app(Old 1.1). Please suggest how can i achieve the above case.

make a new 2nd app and update the old 1.1 (with a new option 'get promotion key' for your new 2.0 app).