Its pretty easy to change out lenses - most frames have the same procedure. The frame is all plastic and just peels away from the lens which is held in a groove.
For lens try to get a bright day lens that has some type of mirror coating - it helps cut down the glare from the sun. I like lens that increase contrast, like a rose tinted lens.
I have Spy optics goggles and run 3 lens. A 15% mirrored bronze for sun, a 40% rose for overcast days and a 70% yellow lens for snowed out days.
The wisdoms are nice, I had a pair with the blue permission colored lens and it worked out pretty well for most conditions. On sunny days it was a bit hard to see, but for overcast days it was fine.