What To Do For The Swelling In The Leg Due To Sun Burn?

I got a bad sunburn on my legs when I went to the beach. My feet are now swollen pretty bad, so bad I can hardly see a definition of my ankle bone. I have tried elevating my feet above heart level and this brings the swelling down but as soon as I walk around for a little bit they swell back up. Can you tell me what I can do to stop the swelling and how long until the swelling will go away?