Easiest way I found was to cut off the plastic part of the old impeller with a 4" angle grinder, then grind off the metal insert within the old impeller on one side so that it is really thin and weakened, then use a large straight crow bar with a flat end and hammer that with a club hammer to lever it off, also used lots of WD40. when grinding off the metal of the old impeller, careful not to grind too deep so as not to damage the shaft.
Ed Willis, June 2019