Lift out the old impeller making sure the TWO thin steel washers underneath the impeller do not fall out. These are very important for the overall height of the lower burr and thus grind fineness.

NOTE: Discard the fibrous felt ring below the impeller. It is usually in pretty bad shape. This piece is no longer needed as the new impeller design hugs the bushing pedestal more closely and does a good enough job keeping grounds away from the bushing and drive shaft.