To replace brush heads:
Pull firmly to remove existing brush head. Align new brush with the square, tapered end of the turbine shaft and push FIRMLY into place.
I bought this replacement brush set simply to have a back-up. The originals (bought a few months back) are still going strong. I simply wanted some extras. I also wanted to try to the long, soft brush that gets into narrow places. I've still yet to try it. Overall, I'm really satisfied with the whole set-up and hope to use it for a long time to come.
Good quality and price with the discount.
Love it but wish I could purchase the stiffest brush (blue) individually, as I don't need the others.....