your actually supposed to take the glass out to do this. just get your fingers behind the glass & gently lever it off. (it only clips on) then there are clips inside holding the covers on, squeeze them together with pliers or similar. if you just rip the covers off the clips are prone to breaking. (got told this by the bodyshop i had my mirrors colour coded at the other week & my local
seat dealer also uses him so he knows what hes on with)