Yes, the inside triangle is the one you are tying to pry off. There is a clip holding it about an inch down from the top of it, having the window down helps. Slip a screw driver in there and toward the top and pry a bit. The top of it pops out toward the driver and then you just lift it out, shouldnt be too hard, and if you break it its no big deal, most likely you will break the clip if anything, which can be glued back on, but most likely if you buy a new mirror then it will come with a new inner triangle with a hole cut out in it for the adjustment, unless you get an electric one. Hope this helps.
1985 190E 2.3-16
1984 280GE Cabrio
1957 220S(running one day, I hope!)