I took my impeller off without any special tool, I had the flat side of the shaft in the vice and since my wear ring was junk anyway and the impeller deffinately wasn't new, i used three pieces of pine wood about 3/4" square and wedged them in between the prop and the wear ring then I was able to turn the whole pump body, prop included. It unscrewed right off. When I put it back on I had some thick gloves and tightened it as much as I could, the way the motor spins it will constantly tighten the impeller as you run it.
I am by no means an expert, just saying what worked for me.