Is it just that the lenses have gone cloudy/yellow Mac, or is the chrome peeling on the inserts?
If it's just yellowing it really is easy, although much much easier if you have a machine polisher - I generally have mine done once a year by a body shop (for buttons, doesn't take them long). Process is wetsand with a very fine grit paper until they go white, then hit with the polisher and a buffing compound. 5 minutes each light and they come up like new.
If the chrome is peeling then they need to be split to correct them, I've done this quite a few times and it's not difficult, the bit that you need to really pay attention to is making sure that they're properly sealed when put back together...and not melting them in the oven obvs