(1) During the lease, the parties may agree an increase in rent.
(2) Future changes in the amount of rent may be agreed by the contractual parties as stepped rent under section 557a or as indexed rent under section 557b.
(3) In all other cases, the lessor may only demand rent increases under the provisions of sections 558 to 560 to the extent that an increase is not excluded by agreement or the exclusion is evident from the circumstances.
(4) A deviating agreement to the disadvantage of the lessee is ineffective.