It is a bit fiddly.
The inner triangular panel has to be prised off carefully. Such a long time ago I did mine, I can't remember if there's anything specific about its direction of removal, sorry.
If it is electric, the inner panel is just a cover. If you have the remote stalk, that, I think, has a retaining ring around it. Finding something to grip it might be challenging.
Once behind the cover, you'll find a large 'nut' holding the mirror on. This is hard work. I used a set of very large circlip pliers, as the legs fitted into the grooves of the nut. Needle nose pliers might also work. This nut is tight, and has little barbs discouraging its undoing, so you have to overcome this resistance all the way off. Much swearing may be needed. And of course, at the same time, you have to support the mirror outside. Refitting is much easier.
Aftermarket mirrors are available, but they were all, (when I upgraded my little ones) for LHD. This puts the glass at maximum adjustment, still showing too much car. If the aftermarket one is not definitely RHD, get an OE.
The mirror has some foam seal where it fits against the door. My aftermarket mirrors came without that. I used some draught excluder strip from B&Q, which seems to have worked well. The adhesive-backed foam strip.
https://www.diy.com/departments/dia...-draught-seal-l-6m-w-9mm-t-5mm/1802898_BQ.prd
