How do I get a renewal of my initial Italian investor immigrant visa?

I read that after an initial investment in Italy, the government grants a two-year resident visa. However, to stay longer and eventually get Italian citizenship, you have to apply for an extension of that two-year visa. How do I apply for this extension? What determines success in the application?

Answers

On Alessia Ajelli answered:

The renewal of the visa can be granted if the investment initially carried out is kept, not withdrawn or changed, even partially.

On Marco Mazzeschi answered:

The renewal of the visa can be granted if the investment initially carried out is kept, not withdrawn or changed, even partially.