You need to have him execute a stock assignment of his shares to you. You would want this stock assignment to include some representations and warranties from him to you, such as -- he owns the shares, hasn't sold them to someone else, etc. But it can be a short document. You may also want that document to include a release of claims, in which he releases you from any claims on the business--such as claims for unpaid salaries or similar amounts. It won't take long for a lawyer to assist you with this, but you should find a lawyer who can help you.