Removing Peugeot 306 Mirror Glass Pate?

i have a 1997 R Reg Peugeot 306

how do i replace just the glass plate without damaging anything as i was told it is glued on or something?

the old one has been cracked ever scince i bought it and i think its time to fix it, looking at a new plate on ebay, just wondering how hard it will be to change it?