As the sole shareholder of a S corp you are free to set up a SEP-IRA and contribute up to 25% of your salary. But I would think that the S-corp would have to start a new plan. Possibly you can roll your existing SEP-IRA over to the new one but this is definitely a question for your plan administrator. Each plan is otherwise separate. 

If you have employees you must contribute to their accounts unless instead of a SEP-IRA you create a single recipient 401k restricted to owner and spouse