Only change a goggle lens if your goggles and hands are completely clean, nothing scratches a lens quicker than dirt and friction! When removing a lens hold the bottom of the frame firmly and grab the top of the frame from the inside and lift the top of the frame away from the lens. Once you have the top section separated you can work your way around the frame until the lens is removed.
To replace the lens you will notice a series of notches around the edge of the lens, these are to be aligned with a series of locating posts inside the groove of the frame. Start with the nose piece and once this has been aligned you can then work your way around the goggles lining each locating post up with the lens and squeezing the frame firmly back onto the lens.