Your reverse cycle air conditioning unit, needs to be run on heat a few times a year to keep it operating perfectly. You may only use the cooling cycle, but it needs to be reversed for heating and long jeopardy of your investment.
You can clean the evaporator (indoor unit on wall) filters by your self, take them out and hose the dust out. Let dry completely, then put them back in.
You can also call a professional to clean your split system, they have all the tools necessary for a total clean, they clean it all, carefully and professionally. The filters are only a small part that requires cleaning. If in doubt, pick up the phone, call a professional.