I had bought a pair of Oakley glasses and went the non-polarized version. They are not cheap in that style,but crafted well  and very user friendly. I decided to upgrade to  polarized and bought polarized lens which are not cheap either. Now I did not know how  easy it would be to swap out the lens from the frames. I went online to check out some recorded help videos. When the lens replacements arrived,I still had to do the task of changing the lens. The lens came delivered with directions that were easy to follow along with the video I saw. Videos that I saw prior to receiving the lens,were hunted down on "YouTube" and offered by non-sponsored people who were experienced enough to download a video to help people like me who knew nothing. Inspect the lens that are delivered,to make sure they are in good shape. The seller of these lens sent a manufactured,sealed order,through Amazon. So check for the professionalism,after all,you paid good money for them. Then get ready for the transition to polarized lens. They enhance your vision with better color intake and that is worth every penny. If I would of bought polarized glasses to begin with,I would saved up to $75.00. So pay attention,not more money.......................Go to YouTube and check out this guy,he is "sterile" about doing the swap-out of lens....search in your browser:"How To Interchange Lenses In Your Oakley Gascans, or Any Other Lifestyle Sunglasses With Dual Lenses
by redskindude324"...you will find other hits in that search,variations of people showing their spin on the task.