1- There is a small rectangular clip on the rear of the lens – push this with your thumb - through to the other side of the lens. Once it is clear lift the lens out of it’s retaining slot.
2- Replace the new lens into the frame (nose end first). Then push the clip back into and through the lens with you thumb.
In order to best demonstrate how the photochromic lenses adjust you can do this simple test.
Start indoors where the light has not affected the lenses.
Place your cupped hand covering half of one lens.
Once half of the lens is covered, take the sunglasses outside & hold the sunglasses up towards the sun.
After 30 seconds to a minute, remove your hand and hold the sunglasses up to light.
You will be able to see a noticeable difference between the covered side (minimum light, dark conditions, indoors) and the uncovered side (full sun)
It is not something that is otherwise noticeable as you are wearing the lenses, as the lenses gradually darken at the same time.
Another important note is that the nose bridges are adjustable.
This means they become a one size fits all and are great for hot days when they can be adjusted up and off the nose.