Get rid of the discoloration of the head light lenses? on 1999 Ford Taurus

How do you remove the yellowing foggy discoloration off the headlight lenses? They are making my headlight beams have a week visual output. I have to keep my lights on high beam just to get a normal lighting at night to see.

Asked by for the 1999 Ford Taurus
Google headlight restoration with your zip-code , there are lots of companies out there that do that now.
I googled headlight restoration and found toothpaste or sandpaper w/water helps for outside. Can you clean the inside of the headlights?