Remove the old lens from the frame and insert the new lens into the frame lens slot starting at the temple area. Continue working the lens into the frame lens slot along the nose. Now engage the lens keyholes into their respective frame retention posts, working from the nose toward the upper frame. It may be necessary to stretch the frame slightly as you progress in order to keep the lens keyholes and frame post lined up properly. Be sure the entire lens is properly seated in the frame slot and all frame retention posts are fully engaged with the lens keyholes.