I did the exact same thing to my i30, basically a Cerato with more boring clothes
You can replace the lens, check out
www.7zap.com for parts fiches and look for the part number on eBay or similar. The best would be to remove the trip on the inside of the door near the mirror base. You should see three nuts holding the mirror assembly off and a cable for the mirror heater and motor assy.
Remove these and take the entire mirror off the car. It's then a case of prying the glass off - there are notches behind the glass that you need to get a small flathead screwdriver into after which it should pop loose. Just be very careful not to break the glass. There may be guides on the various Kia forums.
Then it's a case of systematically disassembling the rest of the mirror which has I think three screws behind the glass you just removed and another one beneath holding the grey shell to the black plastic shell.
Will see if I can find a guide for you