First pull the white nut from the back of the shaft by unscrewing it. Righty tighty--lefty loosy. Then you can slide out the prop shaft with gear and prop. Be very careful not to lose the washer between the bearing and the white nut! Now hold the gear and unscrew the prop from the shaft by turning it to the left looking at the front of the propeller.
Now the fun part. If you're reading any instructions, discard them.
NOT MY INSTRUCTIONS!!!
Screw the new propeller on the shaft until you can't see the threads and the screw bottoms out. Don't overtighten, just go until it stops.
Now reinsert the shaft into the bearing, slide the washer on the back and screw the white nut back on. Only go until there is a couple thousandths of play back and forth, don't try to tighten it to take the play totally out or you'll have too much friction and your battery won't last worth a crap. That's technical language not all will understand, but don't worry about it.
FINALLY (this is where we depart from instructions) without glue, place the spinner on the prop. It will fit with enough friction that you can hook up your battery and turn the motor over at low speed to see if you're perfectly centered. If not tweak and repeat testing. When you're ready a drop of thin CA on a toothpick applied to each side of the spinner where it meets the prop will wick the glue into the joint. Remove excess with the corner of a piece of paper towel if necessary. Don't use kicker because that could ruin your whole day on the rubber and plastic. It will cure in a couple of minutes and go fly!