Remove the old shower-door handle with a screwdriver. Typically two or more screws, installed on the inner handle, hold the two pieces of the handle together with the glass door sandwiched between them.
Inspect and note the differences between the inner and outer shower-door handles. The outer handle has a smooth finish. The inner shower-door handle typically has one or two screw holes.
Orient the outer handle to its functioning position on the outer surface of the shower door. Align the shafts of the handle with the predrilled holes in the glass door. Depending on the handle kit, you may need to place small rubber washers on the ends of the shafts of the handles before screwing them together. Temporarily hold the outer handle in place with a strip of masking tape.
Position the inner handle on the inside of the shower door, opposite the outer handle. Align the shanks of the inner handle to the holes drilled in the glass door and the shanks of the outer door handles. Using a screwdriver and screws provided in the handle kit, screw the inner and outer handles together. Remove the masking tape.