First take off the right side saddlebag. Then, using a 1/4 in 12 point socket, loosen the two pad pins, but don't take them out.
Also take the cap off the rear master cylinder, which is located near the rear brake pedal. Use a phillips screwdriver.
Using a putty knife push the inner pistons back. Watch out that Master cylinder do does not overflow. (The photo shows the outside pistons being pushed back.)
Pull out the two pad pins until the rear pad falls out and put the new one in. Push the pad pins back in and pump the brake. The reason for doing one side at a time is to keep the anti-rattle spring from falling out.
Use the puddy knife and push the outside pistons back and while making sure the inside pads stay in place, pull the pad pins, drop out the old outside pad and slide in the new pad. Put the pad pins back in and torque them to 190 in lbs.. Put the master cylinder cap back on and you are done.