The upper shock mounts on the convertibles are behind the rear seat.  They're in the trunk somewhere for coupes and fastbacks.  The lower part of the rear seat is removed by pulling it upwards at the front.  It should lift right out.  The back portion of the rear seat is removed by removing the two retaining screws at the bottom and then lifting it straight up.

Step 2: Remove The Upper Nuts

The upper shock mounts are located on both sides of the convertible top motor.  Use the socket extension to reach in there easily.  Remove the nut and grommet from the top of each shock.

The shocks mount underneath at the same location as the leaf springs.  Remove the nut and grommet from the lower portion of the shocks.  You may have to use a pair of vise grips to hold the base of the shock if it turns with the nut.

After the nuts are removed compress the shock by pushing the base up until there is enough clearance to remove the shock from the mount.

Installation is the opposite of removal although there are a few things to look out for.  When the shocks are lined up with the mounting points they will be compressed when you climb in the back seat of the car.  After I got them lined up where I wanted them I leaned over the side of the car to get the upper nuts started.  This eliminated the problem of the shocks being moved from the weight in the rear seat area.

The nuts should be tight but don't go overboard with them to the point where the the rubber grommets get crushed.

If nuts from the old shocks are salvageable you may consider putting an extra one on each new shock on the lower end.  The second nut will lock the first one in place and reduce the chance of the nut working loose and falling off.