With your knife, slice through the wide vinyl strap at the very top of the shoulder pads. This will detach the plate from the wide strap that it is riveted to.
With your scissors, cut the one-inch strap that connects the front of the plate to the shoulder pads. It doesn’t matter where you cut it, you will not need to keep this strap for anything.
With your scissors, cut the one-inch strap that connects the back of the plate to the shoulder pads. It doesn’t matter where you cut it, you will not need to keep this strap for anything.
Your plate should now be free from the shoulder pads, and should look something like this.