Not during the exclusive authority period unless your agent agrees, if you have signed an exclusive auction or private sale authority. If the exclusive authority also has a non-exclusive period you can cancel that at any time, by giving your agent written notice.
If you engage the services of another agent on an exclusive basis while you have a current exclusive authority, you may have to pay each a commission on the sale of your property.
If you gave your agent a general sale authority, you can cancel it at any time by giving your agent written notice.
Source: Real Estate Institute of Victoria