The general rule of thumb is that acts are amended (or repealed) by acts and regulations are amended (or repealed) by regulations. Some acts do explicitly state that they can be amended by regulation, although what can be amended is usually minor (e.g. making changes to a schedule to an act).
An example of this can be found in British Columbia’s Workers Compensation Act:
(4.1) The Board may, by regulation,
(a) add to or delete from Schedule B [of the act] a disease that, in the opinion of the Board, is an occupational disease,
(b) add to or delete from Schedule B a process or an industry, and
(c) set terms, conditions and limitations for the purposes of paragraphs (a) and (b).
Such provisions are known as Henry VIII clauses. The name is based on Henry VIII’s reputed fondness “for legislating directly by proclamation rather than through Parliament.”