Be forewarned, on some cars, removing the stock mirror can be very difficult. Some seem to be very securely attached while others slip right off. Applying any strong force with a prying screwdriver is very likely to damage the windshield. Go slow, and be very patient.

If at any point you feel uncomfortable or are applying too much pressure to remove the mirror, take the car to a professional.

Remove the soft or hard top.

Slide the "plinth" cover off, away from the windshield on the top side to gain space to release the retaining clip. You can see the clip from the outside of the car (its silver, visible on the top of the plinth that's glued to the windshield.

Tape together 2 nickels in a stack with a soft tape like duct tape to prevent any sharp metal edges from contacting the windshield.

Gently slide the nickels under the the top of the plinth retaining clip, this will push the clip back, spreading the load across a wide enough area to not damage the windshield.

Once the clip is no longer retaining the mirror, it should slide down off the plinth. Be super patient here, no twisting or prying. If it is particularly stuck you may need to VERY GINGERLY wiggle or tap the base of the mirror. Again, any significant force applied to the plinth will cause damage to the windshield.

Screw the 2 halves of the adapter together (though not completely tight).

Slide the adapter into the windshield plinth and tighten the 2 screws.

The new mirror will slide onto the plinth from the top down.

Tighten the bolt retaining bolt for the mirror.