I had usurped a large amount of money some years ago and started a business which yielded much profit.

Answer

You have to incumbently return the usurped money to its owners. The profit is haraam. It has to be compulsorily given to the poor without niyyat of thawaab. If you wish, you may also give it to the owners of the money which you had usurped and employed to gain the profit. In addition Taubah is Waajib.