(1) Any half-monthly payment payable under this Act, either under an agreement between the parties or under the order of a Commissioner, may be reviewed by the Commissioner, on the application either of the employer or of the *[employee] accompanied by the certificate of a qualified medical practitioner that there has been a change in the condition of the workman or, subject to rules made under this Act, on application made without such certificate.
(2) Any half-monthly payment may, on review under this section, subject to the provisions of this Act, be continued, increased, decreased or ended, or if the accident is found to have resulted in permanent disablement, be converted to the lump sum to which the workman is entitled less any amount which he has already received by way of half-monthly payments.