Disconnect the saw from its power source to prevent it from coming on while you remove the blade.
Rotate the upper blade guard clockwise to move it away from the saw blade an over the saw housing. This exposes enough of the blade that you can lift it out of the housing once you unbolt it.
Wedge a wooden block between the saw blade and the saw blade housing at the bottom of the saw. When you attempt to unbolt the blade it will attempt to turn counterclockwise. The wooden block will prevent it from moving.
Loosen the nut located on the center of the blade with a wrench. Once loosened, thread the nut off the shaft with your fingers.
Slide the blade off the shaft and lift it upward to remove it from the saw.