Except in some highly complex cases that typically do not apply to a small or medium sized business, a company that is set up as a Corporation cannot change that designation to a Limited Liability Company.
To make such a change, the Corporation would need to be dissolved. Then the business owner would be free to set up an LLC as a new entity with the state in which it is to be registered.
To file for either type of corporate status, see details about Standard Legal’s self-help software for Incorporation and Limited Liability Company.