Most of the instructions you find online are for a different type of coupler that pops off. This model is different, as the coupler unscrews.
I found a video for this specific model blender and I'll summarize below:
Turn the blender over so the bottom of the blender is facing up
You have to pop the bottom rubber feet off.
Take off the four screws on the bottom of the blender
Lift the bottom of the blender up and off.
This may take two people.
You'll need a heavy duty wrench under the blender to lock down and secure the coupler to keep it from spinning.
You'll need a flathead screw driver to turn the screw that is on the Fan that is on the bottom side of the blender. Please note the threads are reverse so you have to turn the screw to the right to loosen. I repeat to the right to loosen. While holding The coupler from moving. ( there's no reason why they had to make that screw so small, it made it almost impossible to take off. Not very user-friendly…)
Once it's loosened turn it back over and unscrew the coupler.
Screw the new coupler on.
Reverse the steps to put the blender back together.