They stick on over the existing mirrors. If you want a cleaner finish, then you can remove the double sided tape beforehand and use silicone caulk to attach them.
You can't really remove the old mirrors and replace with the multivex ones because they are convex and won't fit flush in the existing mirror housing.
Edit:
Ace10 sent me a link to this post outlining how to install them with less protruding edges by removing the old mirrors:
Multivex Mirror review