How do I change the flywheel key and blad adapter on my briggs and stratton?

The flywheel key is in a slot which lines the flywheel to the correct position on the shaft, you need to remove the flywheel to get at it ( they are usually "D" shaped),if you remove the flywheel nut,(left hand thread) you may be able to see it under there and if you can see it you will be able to see if it has sheared.
I suspect all you need to do is replace the blade as it will now be out of balance and that is why your machine is vibrating and difficult.

Ed.
May 2007