Can I upgrade from Iphone 5c to 5s?

I recently joined a plan with t mobile and was offered the choice of an iphone 5c (50 dollars) or 5s (260 dollars) so I opted for the 5c. I want to get an iphone 5s what would I have to do to upgrade? Can I trade it in for cash and use that to buy the 5s? Also would it still be offered at 260?

YOU DON'T DESERVE