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You mean you want to try to get the lens seperate form the rest of the housing? It can be done, but you'll need an oven. If you mean just getting them off of the truck, there are two tabs for eack light. They are above and behind the light when you open the hood, on either side. Pull them up right at an inch.
Most likely you just need to clean/refinish the exterior of the lens. I reworked the lights on my dad's van a couple weeks ago. Bought a kit in the automotive section at Walmart for $20. It's in a mylar looking pouch. It has compounds, sandpapers, some "magic cloth" and a clear coating for the final step. They turned out WAY better than I expected them to. Anything more than 5 feet and the pretty well look brand new, they were seriously yellowed too. It didn't get out all the bigger nicks, but they are as clear as ever and putting out much more light. Good luck.
I tried the toothpaste route, even "whitening", and had mediocre results. It never got them anywhere near new looking. What good it did do didn't last very long either, I'm hoping the clear coat in the kit I used will last a while.