Vacuum cleaner filters perform two functions, they keep dust from being kicked back into the air, and they protect the motor. If your filters are dirty, your vacuum's motor may be overheating, and you may not be getting as the deep clean you thought. Dyson recommend washing your cyclonic filter once every 6 months.
Safety first: disconnect your vacuum cleaner from the power supply before performing this procedure.
Remove the filter container
Unclip and open the filter cover, and carefully lift out the circular filter container, before removing the foam
Wash with a mild detergent, rinse and allow to completely dry before replacing.